Use Cases and Scenarios.

List of actions or event steps, typically defining the interactions between a role (known in the Unified Modeling Language as an actor) and a system, to achieve a goal.

Use caseWikipedia
Understanding Use Case AnalysisUX MotelFebruary 25th, 2014
Posts about Use cases on UX ApprenticeUX ApprenticeDecember 19th, 2011
Use Case 2.0 eBook (download)Ivar Jacobson InternationalDecember 14th, 2011
What Are Use Case Scenarios?Tyner BlainApril 10th, 2007