Yumex GUI Question about version numbers

[Jonathan Ryshpan]

Some version entries on the Install screen of are of the form
<number>:<version>, e.g.

+  Package  Ver                  Summary      ...
        gg2      3:2.2.8-2.i386.rpm   GNU Gadu 2   19-Oct-2005 22:00
        164k
                 ^

In this case the line starts with a (large green) plus, which (I think)
indicates that this is a recent entry in the repository, and the number
referred to above is a 3.  What does this 3 indicate?

Thanks - jon