What is Use Case Modeling ?

What are Use Cases and what is Use Case Modeling ?
A use case is a technique used in software and systems engineering to capture the functional requirements of a system. Use cases describe the interaction between a primary actor—the initiator of the interaction—and the system itself, represented as a sequence of simple steps. A Use Case represents a discrete unit of interaction between a user (human or machine) and the system. This interaction is a single unit of meaningful work, such as Create Account or View Account Details.
Actors are something or someone which exist outside the system under study, and who (or which) take part in a sequence of activities in a dialogue with the system, to achieve some goal: they may be end users, other systems, or hardware devices. Each use case is a complete series of events, from the point of view of the actor
A Use Case Model describes the proposed functionality of a new system. Use case modeling helps developers to capture user requirements. Use Case Modeling is sure to give development teams the tools they need to translate vision and creativity into systems that satisfy the most rigorous user demands.
Use case modeling from the user model view (also known as the use case or scenario view), which encompasses a problem and solution as understood by those individuals whose problem the solution addresses, involves use case diagrams to depict the functionality of a system.