Regression testing is any new features added to the 
application,then you have to do the regression testing.
Why Automation is apperantely used for Regression,at the 
time of doing regression testing, application is 
stable.Allready you loged the somany bugs,which is doing 
new feature testion.

retesting the entire application after the debugging,is 
called regression testing. In winnrunner we r using batch 
test for testing the entire application

We do RegressionTesting whenevr thr are new enhancements in 
the module of the application or an integration of new 
application with existing one  or whenerv a bug is fixed 
then we go for this kind of testing.
so,that added features /bug fixing didnt adversely affect 
the currently running application.
we do this kind of testing in between builds.
Usually for regression testing we write testcases for added 
feature modules.usually in companies they maintain 
checklists for important functionality testcases ,bcoz 
during regression testing we dont find ample time to test 
all the testcases.
Regression Testing Tools(also frequently called 
Functionality Testing tools)...we use Winrunner,QTP,...many 
more tools.
-->we usually automate the test scripts using ur testcases.
-->We enhance the scripts by adding wait 
statements,synchronization points,checkpoints,regular 
expressions,functions,recovery manager(to handle 
exceptions) only after WR7.6 VERSION,virtual object wizard
(for non-standard objects)  and many more...
All this to run until the error free scripts.
If any errors found,reporting the defects to developers 
through test director or PVCS OR any bug tracking tool ur 
company using.

re testing the application after fixes or modification to 
ensure the effect of regressed part on the remaining 
functionality of the application.

in winrunner by making use of RAPIDTEST SCRIPT WIZARD we 
can conduct GUI regression ,Bitmap regression.

Reexecution of same application in different releases,to 
just  ensure that the changes i.e
(addition,deletion,modification or bug fixing) have not 
introduce any defects in the unchanged features