What is acceptance testing?

In software development, user acceptance testing (UAT) - also called beta testing, application testing, and end user testing - is a phase of software development in which the software is tested in the "real world" by the intended audience. UAT can be done by in-house testing in which volunteers or paid test subjects use the software or, more typically for widely-distributed software, by making the test version available for downloading and free trial over the Web. The experiences of the early users are forwarded back to the developers who make final changes before releasing the software commercial.

Most of the time it is tested by beta tester or end user(depends on company policy)  to know if the application is working as expected.

Testing which is done to enable the customer/user whether to accept the product or not. it is done by end users.