For many uses of CVS, one doesn't need to worry
too much about revision numbers; CVS assigns
numbers such as
1.2, and so on, and
that is all one needs to know. However, some people
prefer to have more knowledge and control concerning
how CVS assigns revision numbers.
If one wants to keep track of a set of revisions
involving more than one file, such as which revisions
went into a particular release, one uses a tag,
which is a symbolic revision which can be assigned to a
numeric revision in each file.