The ISO standards provide a long series of definitions of the term service - which seems rather strange for an organization that claims to provide standards. Nevertheless, this is a list of 100 options you can choose from:

  1. ISO/IEC Guide 14:2003 - result of activities between a supplier and a client, and the internal activities carried out by the supplier to meet the requirements of the client
  2. ISO/IEC Guide 76:2008 - result of at least one activity, necessarily performed at the interface between the supplier and customer, that is generally intangible
  3. ISO 834-9:2003 - devices penetrating the ceiling (e.g. lighting and ventilation systems) not otherwise covered by a specific fire test
  4. ISO/IEC 2382:2015 - <open systems interconnection> capability of a given layer and the layers below it that is provided to the entities of the next higher layer
  5. ISO/IEC 2382-36:2019 - output of an organization with at least one activity necessarily performed between the organization and the customer [taken from ISO 9000:2015]
  6. ISO 3534-2:2006 - product that is the result of at least one activity performed at the interface between the supplier and the customer
  7. ISO 4254-1;2013 - activities to be done as required and/or at regular intervals by an operator familiar with the machine characteristics and complying with the information for service and safe practices, as specified by the manufacturer in the operator's manual and by signs on the machine, in order to maintain the proper function of the machine
  8. ISO 5127:2017 - means of delivering value for the customer by facilitating results the customer wants to achieve [taken from ISO/IEC 20000:2011]
  9. ISO 6707-1:2017 - system for conveying water, gas, warm air, or electricity, or that provides water, gas, oil, or air to or within a construction works (3.1.1.1) or removes waste (3.8.13) from it
  10. ISO 8927:1991 - all activities necessary to retain an item in operational condition or to restore a failed item. Service is a generic term of maintenance and repair.
  11. ISO 9000:2015 - output of an organization with at least one activity necessarily performed between the organization and the customer
  12. ISO/IEC 9040:1997 - A distinct part of the total VT Service that is composed of a sequence of primitives taken from the set {request primitive, indication primitive, response primitive, confirm primitive}.
  13. ISO 9241-11:2018 and 220:2019 - means of delivering value for the customer by facilitating results the customer wants to achieve
  14. ISO 9314-2 and -7:1989 and -5:1995- A set of functions provided by one OSI layer (or) sub-layer entity, for use by a higher layer or sub-layer entity or by management entities.
  15. ISO 9314-9:2000 - FDDI services provided by one FDDI entity to another
  16. ISO/IEC 10027;1990 and ISO/IEC TR 10032:2003 - a capability provided by a processor to other processors, or by a process to other processes
  17. ISO/IEEE 11073-10201:2004 - A specific behavior that a communication party in a specific role is responsible for exhibiting.
  18. ISO/IEEE 11073-20702:2018 -A software system that exposes its capabilities by receiving and/or sending MESSAGEs on one or several network endpoints
  19. ISO 11135:2014 - supplies from an external source, needed for the correct function of equipment
  20. ISO 11336-1:2012: description of the service limitations for which a yacht is assessed to be suitable
  21. ISO 11137-1:2006 - supplies from an external source, needed for the function of equipment
  22. ISO 11139:2018 - supplies from an external source needed for the function of equipment
  23. ISO 11553-1:2005 –(corrective maintenance) performance of those procedures or adjustments described in the manufacturer's service instructions which may affect any aspect of a product's performance
  24. ISO/TS 11602-2:2010 - process that includes maintenance, recharging or hydrostatic testing, or more than one of these
  25. ISO 12967-1 & ISO/TR 12773-2:2009 - number of processes, involving an organization in the provision of specific objectives
  26. ISO 13009:2015 - provision specifically to individuals or groups of individuals in order to facilitate activities of public use
  27. ISO/IEC 13066:2011 and -3:2012 and -4:2015 - functionality made available to a user electronically
  28. ISO/IEC 13157-1:2014 - (N)-service as specified in ISO/IEC 7498-1
  29. ISO 13537:2010 - A service is a provision of an interface of an object to support actions of another object.
  30. ISO 13578:2017 - periodic exchange of lances, cleaning (e.g. lance, slag door area), lubrication, adjustment of limit switches
  31. ISO/IEC 13818-6:1998 - A set of elementary streams offered to the user as a program. They are related by a common synchronization. They may be made of different data, eg. video, audio, subtitles, other data.
  32. ISO/IEC 14165-372:2011 and -414:2007 - a service is provided by a node, accessible via an N_Port that is addressed by a WKA or an N_Port identifier (for example, the directory service and the alias service); a service provides access to one or more servers
  33. ISO/TR 14292:2012 & ISO/TR 20055:2018 - ability of a system to provide a defined set of output information based on a defined set of input information
  34. ISO/IEC TR 14369:2018 - facility, or set of facilities, made available to service users through an interface
  35. ISO/IEC 14496-6:2000 - Is an entity identified by a Service Name (opaque to DMIF) which responds to DAI primitives.
  36. ISO/IEC 14772-2:2004 - The method of interfacing between external applications and the browser.
  37. ISO/IEC 14776-411 -412 -413 and -414:1999 and 2007 and 2009 - any operation or function performed by a SCSI object that is invoked by other SCSI objects
  38. ISO 14813-5:2020 - <ITS> performance of one or more tasks that fulfills an ITS user need for an ITS user
  39. ISO 15143-1:2010 - beneficial performance conferred by the system in order to achieve the project goals
  40. ISO/IEC/IEEE 15288:2015 & ISO/IEC/IEEE 15939;2017 - performance of activities, work or duties
  41. ISO/IEC 16500-1 and -7:1999 - A set of elementary streams offered to the user as a program. They are related by a common synchronization. They may be made of different data, eg. video, audio, subtitles, other data.
  42. ISO/IEC 17020;2012 - result of at least one activity necessarily performed at the interface between the supplier and the customer, which is generally intangible
  43. ISO/IEC TR 17028:2017 - output of a service provider with at least one activity necessarily performed between the service provider and the customer
  44. ISO 17215-2:2014 - logical combination of zero or more methods, zero or more fields, and zero or more events
  45. ISO 17264:2009 - road transport related facility provided by a service provider
  46. ISO17267:2009 - data model entity for a commercial activity of interest to travelers as a destination and/or orientation that is associated with road element(s) by which it can be accessed and further described by attributes including (at least) name and type
  47. ISO 17361:2015 - class of links with a common application between typed sources and typed targets
  48. ISO/TR 17522:2015 - specific behavior that a communication party in a specific role is responsible for exhibiting
  49. ISO 17842:2015 - replacement or replenishment of components, including fluids which are designated to be replaced or replenished at specified intervals
  50. ISO 17987-3:2016 - combination of a diagnostic request and response
  51. ISO/IEC 18018:2003 - Abstract description of work done by CM tools.
  52. ISO/IEC TR 18053:2000 - A benefit provided by one CSTA application process to another.
  53. ISO 18091:2019 - <local government> output of a local government process that has at least one activity performed at the interface between the local government and customer/citizen and that is generally intangible
  54. ISO/TS 18101-1:2019 - repeatable business activity that has a specified outcome
  55. ISO 18202:2015 - A set of capabilities that a component provides to another component via an interface.
  56. ISO 18308:2011 - set of related software functionality
  57. ISO/IEC 18384-1:2016 - logical representation of a set of activities that has specified outcomes, is self-contained, may be composed of other services, and is a “black box” to consumers of the service
  58. ISO 19101-1:2004 and -2:2018 and ISO 19103:2015 and ISO 19115-1:2014 and ISO 19119:2005 and :2016 and ISO 19128:2005 and ISO/TS 19129:2009 and 19132:2007 and ISO 19142:2010 and ISO 19143:2010 and ISO 19154:2014 and ISO 19155:2012 and ISO 19167:2019 - distinct part of the functionality that is provided by an entity through interfaces
  59. ISO/TR 19231:2014 - ability of a system to provide a set of output information based on a defined set of input information
  60. ISO/IEC 19762:2016 - software program that provides responses to requests from other software programs, which are frequently on other remotely connected computers
  61. ISO 19763-5 and -7 and -9:2015 - kind of application which encapsulates one or more computing modules and can be accessed through a specified interface
  62. ISO/IEC 19790;2012 - any externally operator invoked operation and/or function that can be performed by a cryptographic module
  63. ISO/IEC 20000-1:2011 and -10:2018 - means of delivering value for the customer by facilitating results (or outcomes) the customer wants to achieve
  64. ISO 20106:2015 - A set of capabilities that a component provides to another component via an interface.
  65. ISO 20400:2017 - results generated by activities at the interface between a supplier (3.30) and a customer and by supplier internal activities to meet customer needs
  66. ISO/TS 20452:2007 - data model entity for a commercial activity of interest to travelers as a destination and/or orientation that is associated with road element(s), by which it can be accessed, and place(s)
  67. ISO/TR 20514:2005 - number of processes, involving an organization in the provision of specific objectives
  68. ISO 20534:2018 - system function that plays the role of a product
  69. ISO 21219-1 and -9 and -10 and -19:2016 - collection of different information streams (applications) logically bound together and delivered from a service provider to the end user
  70. ISO/IEC/IEEE 21451-1:2010 - An instance of a subclass of IEEE1451_Service
  71. ISO/TR 21245:2018 - result of activities between a supplier (3.23) and a customer, and the internal activities carried out by the supplier to meet the requirements of the customer
  72. ISO 22301:2012 & ISO/TS 22318;2015 - beneficial outcomes provided by an organization to its customers, recipients and interested parties, e.g. manufactured items, car insurance and community nursing
  73. ISO 22902-1:2006 - software that provides a useful function to another entity
  74. ISO 23006-2 and -4 and -6:2016 - operation performed on an entity by a user on behalf of other users
  75. ISO 23007-1:2010 - system supporting interaction, local or over a network, by means of message exchanges (e.g. UPnP service or Web service)
  76. ISO 23950: 1998 - (1) A Z39.50 service, as in the "search" service; (2) an extended service, as in the "persistent result set extended service"; (3) the service-provider.
  77. ISO 24510:2007 and ISO 24511:2007 and ISO 24512:2007 and ISO 24516:2017 and ISO 24520:2017 - result of a process [Adapted from the definition of “product” in ISO 9000:2005]
  78. ISO 24516-1:2016 - result of a process [adapted from ISO 9000:2005]. Service is the result of at least one activity necessarily performed at the interface between the provider of the service and, in the first place, its user and, in the second place, a stakeholder. The word “service” in common English can also refer to the entity providing the actions related to the subject in question, as is implicit in such phrases as “bus service”, “police service”, “fire service” and “water or wastewater service”. In this context and usage, “service” implies the entity that is delivering the service, e.g. “the public transport of passengers”, “the provision of public security”, “fire protection and response”, and “delivering drinking water or collecting wastewater”. If “service” can be understood in this way, “water service” becomes synonymous with “water utility”; hence in this document, in order to avoid confusion, only the definition in 3.19 applies. [from ISO 24510:2007]
  79. ISO 24516-4:2019 and ISO 24513;2019 - output of an organization with at least one activity performed between the organization and, in the first place, its user and, in the second place, a stakeholder
  80. ISO/IEC 24727-1:2014 - set of processing functions available at an interface
  81. ISO/IEC 24748:2006 - performance of activities, work, or duties associated with a product.
  82. ISO/IEC 24752-1:2014 – functionality made available to a user electronically
  83. ISO 24752-8:2018 - server offering RESTful operations for the management of REST resources
  84. ISO/IEC/IEEE 24765:2017 - means of delivering value for the customer by facilitating results the customer wants to achieve 2. performance of activities, work, or duties [ISO/IEC/IEEE 15939:2017 Systems and software engineering — Measurement process, 3.35; ISO/IEC TS 24748-1:2016 Systems and software engineering — Life cycle management — Part 1: Guide for life cycle management, 2.46; ISO/IEC/IEEE 15288:2015 Systems and software engineering — System life cycle processes, 4.1.42]3. behavior, triggered by an interaction, which adds value for the service users by creating, modifying, or consuming information; the changes become visible in the service provider's environment [ISO/IEC 10746-2:2009 Information technology — Open Distributed Processing — Reference Model: Foundations, 13.3.1] product, result, deliverable
  85. ISO/IEC 25011:2017 and ISO 25065:2019 - means of delivering value for the customer by facilitating results the customer wants to achieve
  86. ISO 25424:2018 - supplies from an external source needed for the function of equipment
  87. ISO 26000:2010 - action of an organization to meet a demand or need
  88. ISO 27501:2019 - means of delivering value for the stakeholder by facilitating results which the stakeholder wants to achieve
  89. ISO/TS 27790:2009 - specific behavior that a communication party in a specific role is responsible for exhibiting
  90. ISO/IEC TR 29108:2013 - Logical functional unit. Smallest units of control. Exposes actions and models the state of a physical device with state variables. For more information, see clause on Control (in ISO/IEC 29341-1)
  91. ISO/IEC TR 29110-1:2016 - performance of activities, work, or duties
  92. ISO/IEC 29110-4-4:2018 - A set of functions provided by one OSI layer or sublayer entity, for use by a higher layer or sublayer entity or by management entities. Data services are provided to a higher layer or sub-layer entity; management services are provided to a management entity. [taken from ISO/IEC/IEEE 15288:2015]
  93. ISO/IEC TR 29110-5-3:2018 - performance of activities, work or duties
  94. ISO 30100-1 and -2:2016 - field of use of an HES
  95. ISO/IEC TR 30102:2012 - logical representation of a set of repeatable activities that has specified outcomes, is self-contained, may be composed of other services, and is a “black box” to consumers of the service
  96. ISO/IEC TR 30109:2015 - software program that provides responses to requests from other software programs, which are frequently on other remotely connected computers
  97. ISO 37500:2014 - result of activities performed by the provider according to the agreed scope, service levels and client demands
  98. ISO/IEC 40180:2017 and ISO 9001:2015- output of an organization with at least one activity necessarily performed between the organization and the customer
  99. ISO 41011:2017 - time-perishable, intangible activity performed for an entity
  100. ISO 50007:2017 - output of an organization with at least one activity necessarily performed between the organization and the customer [taken from ISO 900:2015]

These definitions mostly describe 'service' as one or more of the following entities: activities, processes, output, product, means, system, functions, capability, behavior, supplies, performance, provision, functionality, ability, facility, entity, method, operation, work, benefit, software, results, action, application.

A great example of how inconsistent standards can be...

The most universal definition of a service is delivered by USM: "a service is a supported facility". A facility is defined as a combination of goods and activities. The support is defined in the USM Customer-Provider Interaction Model. This unique definition is one of the building blocks of the USM service management architecture.

PS - if you think you've seen them all, you may run into this very recent definition of 'service':

“Service is the act of integrating and applying competences and other resources by two or more parties within dynamic service ecosystems, with the intent to co-create value, with a focus on relationship-building, and with consideration of the context-dependent, unique and phenomenological nature of value from service.” [Quote from Reflections on XLA].

Check the USM Wiki for more »