it is final stage application testing 
 it is used to check application meets the requirements 
provided

this is the final test as my friend hari said but this is
the crusial test as we will check all the bussiness
requirementrs are full filled by the project or not. from
the plat form to the pin point of the project no excess
works are done etc

UAT stands for User acceptance testing where the
application/system is tested at the customer place or
environ ment, custmer and with assistance of the development
team will carry the UAT is carried by Pilot testing-installs
the system on experimental basis,and the system is evaluated
on daily working basis.

some time system is piloted in house i.e in company itself
before customer runs the real pilot test. this is called as
alpha testing, and customer pilot is called as Beta testing

UAT :User Acceptence Testing final stage of testing this 
testing is done by the client at the developer site to test 
weather that final bulid is meets the customer reqiremts 
(or)satisfy the coustomer needs or not.they are two types 
of UAT 1.Alpha Testing
        2.Beta T esting
1:Alpha testing is done by the customer at developer site 
to know weather the final  build is as per the requirement 
or not.

2.Beta Testing:This testing is done by the end users at 
client side to know weather the system i working as per the 
requiement or not.