functionality testing : here, we wil check the 
functionality of the application.
regression testing: here, we wil check whether all bugs are 
fixed or not by developers & any new bugs are raised by 
fixing of new bugs.

Functionality testing means to Check the Behavior of the 
application
Regression testing means retesting the modified Build is 
called regression testing

F.testing== A major part of black box testing is 
f.testing.testing team more concentrate on these f.testing. 
For ex == any application the basic functionality will be 
like these. If u click on minimized button it will be 
minimized. If u click on submit button it will be go to the 
next page  

Regression testing== in any application new funcnality can 
be added so the application has to be tested to see whether 
the added funcnality are affected to the exciting 
funcnality or not. In other words when the bug where fixed 
by the developer. we have to test that application to 
ensure that to check that due to bug fixing there will be 
profanity of accruing some other bug else where in the 
programme.

Functionality Testing: To test the basic functionality of 
the application. It's called as Functional testing.

Regression Testing: Regression testing should be done to 
make sure that existing functionalities is not broken becoz 
of fixing new code or bug.

Functional Testing as good as System 
behaviour/functionality testing and also known as Black Box 
(Enter Data/info in Client side and see the expected Output 
on Screen or output devices.

Regression is re-do the same as above but after adding new 
functionality/module to see whether any more bugs can be 
found and also see that previous functionality is still 
same as agreed.