Synopsis: release [OPTIONS] DIRECTORY
Cancels a checkout (indicates that a working copy is no longer in use). Unlike most CVS commands that operate on a working copy, this one is not invoked from within the working copy but from directly above it (in its parent directory). You either have to set your CVSROOT environment variable or use the -d global option, as CVS will not be able to find out the repository from the working copy.
Using release is never necessary. Because CVS doesn't normally do locking, you can just remove your working copy.
However, if you have uncommitted changes in your working copy or you want your cessation of work to be noted in the CVSROOT/history file (see the history command), you should use release. CVS first checks for any uncommitted changes; if there are any, it warns you and prompts for continuation. Once the working copy is actually released, that fact is recorded in the repository's CVSROOT/history file.
If you created any new directories inside your working copy but did not add them to the repository, they are deleted along with the rest of the working copy, if you specified the -d flag.