Acceptance Testing (UAT) : This is the most important type of testing as it is conducted by the Quality Assurance Team who will indicate whether the application meets the intended specifications & satisfies the client requirements.
This is the last phase of software testing process in which software tested in "real world" by the specification.This is used when new developed software rolled out to market.
UAT is also called beta testing , end user testing & application testing.

Following types of acceptance testing are :

Alpha Testing:

Alpha testing is final testing done by the developers' sites,and involves testing of the operational system by internal team, before it is released to external customers. It has two phases:

*In the first phase of alpha testing, the software is tested by in-house developers. They use either debugger software, or hardware-assisted debuggers. The goal is to catch bugs quickly.
*In the second phase of alpha testing, the software is handed over to the software QA Team, for additional testing in an environment that is similar to the intended use.

Beta Testing: This testing is performed after Alpha testing has been successfully performed.Beta testing is done by customers' sites, and involves testing by a group of customers who use the system at their own locations and provide feedback, before the system is released to other customers.