Retesting- Re test the defects after fixing by developers.
Regression testing-- Nothing but retest, checking the 
functionality when the status was fixed by developer, the 
latest fixed functionality is effecting the other funcation or 
not & the current funcation is working properly or not.
 

Retesting :  Testing the application on the same built 
soppose tester found the bugs and developer fixed it. 
tested the fixed issues on the same built is called 
retesting.
Regression:  Testing the application on the different built 
Suppose: if the tester found the bugs, and Developer fixed 
it and they relised the new version of the build. so 
testing on the new version on the built is called Regerssion
Testing

re testing:testing the build with multiple test data
regression testing:if the tester find any defect he /she
inform this defect to development team.developement team
fixes that bug, aagin send to the testing team for testing
again whether bug is fixed or not,or the newly developed
build giving any side affects to other modules or not.

Re Testing: Once the Bug is fixed Tester has to test the 
same bug with multiple number of times with different data 
and different scenario. Also once tester find the bug he 
has to test multiple number of times bcoz whether the bug 
is reproduceable or not.

Regression Testing: Once the Bug is fixed tester has to 
test whether bug is fixed or not also test whether the 
impact of the bug is shows in other application

Re-Testing :after the bug was fixed the Test Engineer Re 
execute the failed testcases to check whether the bug was 
fixed or not.
Regression Testing : some times Reexecute some selected 
passed testcases also to check whether are there any side 
affects during the bug was fixed

Retesting  :     Testing the application again in the same  
                    testing conditions ie.same  testing
                    environments.
Regression testing : Retesting the application after fixing 
the defects.

Retesting:
If a tester finds a bug and after developer fixes that bug 
we once again do the testing in order to check the 
validation of the bug fixing.

Regession:
If a tester finds a bug and after developer fixes that bug 
we retest and also check whether these enhancements or bug 
fixing have any side affects on the unchanged code.

retesting is testing the same build with multiple test data.

where as regression testing is done after the bug fixes or 
after any enhancements are done.in regression testing we 
not only test the test case where the defect was found but 
we also check some related test cases to make sure if the 
fix or enhancement has affected any related functionality.
this is done on the new build after bug fixes or 
enhancements

Regression Testing :
                  testing is done to ensure that does not 
affect the other module or unit.
 
Re Test: (retset the module)
        test engineer find the bug.after developer fix that 
bug .test engineer check they fix proper or not......

in any application new funcunality can be added so the 
application has to be tested to see whether the added 
funcunality are affected to the existing funcunality are 
not.
in other words when the bugs where fixed by the developers 
we have to test that application due to bug fixing there 
will be a proabality of accruing some other bugs else where 
in the program.
Retesting means Execution of test with multiple test data 
to validate this function is called as retesting

Regression Testing: Testing of a previously tested program
following modification to ensure that defects have not been
introduced or uncovered in unchanged areas of the software,
as a result of the changes made. It is performed when the
software or its environment is
changed.

re-testing: Testing that runs test cases that failed the
last time they were run, in order to verify the success of
corrective actions.