Difference between User Acceptance Testing & Usability Testing
User acceptance testing (UAT), considered to be the last step before final product release, has been in play for many years. Sometimes it becomes synonymous with beta testing, which is also conducted at the user site. UAT reaches a wide audience of users, allowing the development team to get feedback on how well the system really meets user expectations and how readily the users take to it.
Usability testing, which often precedes UAT, is a relatively new concept. It was introduced as a formal procedure in the late 1980s and began to achieve widespread use in the mid-1990s. Usability testing is typically conducted in a laboratory where users perform normal tasks and usability specialists record observations. It is a technology-driven approach in that screen images of the application under evaluation are videoed, as are the user's body language and hand movements. Users also provide feedback in the form of satisfaction ratings and comments/suggestions on an evaluation form. [Source]
Also See:
User Acceptance Testing
What is Usability Testing