Acceptance Testing is one Phase in a Project, where the Project may be:

• Development and implementation of a new, custom-built system;
• Implementation of a new system based on a package (with or without modifications); or
• Minor or major upgrades to an existing system.

Acceptance Testing is independent of the system development process and performed by end-users and stakeholders before formally accepting the delivered product.

It is where the system is tested to ensure it meets all specified requirements of the system.  These requirements are usually determined prior to the sytem being purchased and/or implemented.