[OASIS] A service is a mechanism to enable access to one or more capabilities, where the access is provided using a prescribed interface and is exercised consistent with constraints and policies as specified by the service description.
[OPEN GROUP] A service is a logical representation of a repeatable activity that has a specified outcome. It is self-contained and is a ?black box? to its consumers.
[OMG] A service is value delivered to another through a well-defined interface and available to a community (which may be the general public). A service results in work provided to one by another.
[ISO/IEC 20000] A service is a means of delivering value for the customer by facilitating results the customer wants to achieve.