User Acceptance Testing (UAT) is a process to obtain confirmation that a system meets mutually agreed-upon requirements. A Subject Matter Expert (SME), preferably the owner or client of the object under test, provides such confirmation after trial or review. wikipedia.org

A bug tracking system or defect tracking system is a software application that keeps track of reported software bugs in software development projects. It may be regarded as a type of issue tracking system. wikipedia.org

Functional testing is a type of black box testing that bases its test cases on the specifications of the software component under test. Functions are tested by feeding them input and examining the output, and internal program structure is rarely considered (Not like in white-box wikipedia.org

Software testing is an investigation conducted to provide stakeholders with information about the quality of the product or service under test. wikipedia.org

Regression testing is any type of software testing that seeks to uncover new errors, or regressions, in existing functionality after changes have been made to a system, such as functional enhancements, patches or configuration changes.

Usability testing is a technique used in user-centered interaction design to evaluate a product by testing it on users. This can be seen as an irreplaceable usability practice, since it gives direct input on how real users use the system. wikipedia.org

Manual testing is the process of manually testing software for defects. It requires a tester to play the role of an end user, and use most of all features of the application to ensure correct behavior. wikipedia.org