This is a Change Control mechanism for managing changing 
changes/enhancements outside the scope of a particular 
project or release you are working on.

E.g I'm working on project A, with requirements H,K,L,P.
These are all the requirements we budgeted for for this 
realese anything outside of it is scope screep and thus 
will require a change request for it to be included at a 
later stage and properly managed and tracked.

After the design signoff is over if clients needs some thing
to be implemented so this will come under the change  request

So the we have to prepare the change control log for the 
change request and send the client  for approval.

CR means the Change Request.

When customet require more or changed the current 
requrement they will raise the CR for the previous releases.

If we are finding the bug in previous relases but still it 
is not closed. after fixing the bug after some releases 
they will raise the CR to test for the bug or the defect 
functionality.