Acronym for Concurrent Versions System, a VersionControlSystem. (Not to be confused with CSV.)
It was born as a batch of Shell scripts wrapping RCS and diff3(1), but evolved into something much greater. Unfortunately, its roots also imply some annoying limitations like being unable to rename/move files in the repository without losing the associated history.
See also:
Open Source Development with CVS by Coriolis Open Press.
Note that some (irrelevant?) chapters regarding the philosophy behind CVS in OpenSource are only present in the printed edition.
A message such as
2402/path/to/repository: no such repository
means that your client is older than version 1.11.x and doesn't understand host:port being part of the pserver path (eg cvs -d :pserver:hostname:2402/path/to/repository). You need to upgrade.
30 pages link to CVS:
lib/main.php:944: Notice: PageInfo: Cannot find action page