It is done on the new build .When u get the new version 
then we will execute the defects on the new build to check 
whether the defects are closed or not.

Regression test can be done as below:
1) Execute all the basic/major functionalities in the 
previous modules.
2) Test the newly delivered module.
3) Check for any integration points between the old and new 
modules.
4) Test the application with all sorts(valid+invalid) of 
data.

Regression testing mean when ever there is a change or bug 
is fixed then to make sure that the changes or fixing the 
bug didn't affect any other functionality of the 
application. To make sure, they run the application again 
and again. It's the same thing in performance testing. To 
make sure the applications is performing it functionalily 
or performance issue they conduct the regression testing.