A sofware design artifact first used extensively in Objectory and later incorporated into UML. The definition of a use case is: "A use case defines a set of use-case instances, where each instance is a sequence of actions a system performs that yields an observable result of value to a particular actor."

A use case describes, from a user's perspective, a behaviourally related set of transactions that are normally performed together to produce some value for the user. Use cases can be represented graphically in a a use case diagram as an oval shape, each use case being described in the data dictionary. Use cases may be modelled at varying degrees of abstraction: essential use cases, the most abstract, are technologically and implementation independent whereas real use cases describe how the use case actually operates in a particular environment.

Source: Bennet, S (1999) Object-Oriented Systems Analysis and Design using UML. McGraw Hill, Great Britain.