cvs-cvsroot is a variable defined in `pcvs-defs.el'.
Its value is

Specifies where the (current) cvs master repository is.
Overrides the environment variable $CVSROOT by sending " -d dir" to
all CVS commands. This switch is useful if you have multiple CVS
repositories. It can be set interactively with M-x cvs-change-cvsroot.
There is no need to set this if $CVSROOT is set to a correct value.