Leading number in package names when updating with yum

[Bruno Wolff III]

On Wed, Feb 17, 2010 at 08:26:43 +0100,
  Joachim Backes <joachim.backes at rhrk.uni-kl.de> wrote:
> Hi all,
> 
> can somebody explain what the leading number in some package names
> means when running "yum update", for example
> 
> Feb 17 07:25:19 Updated: 1:openoffice.org-calc-3.1.1-19.26.fc12.i686

It's the epoch.