Updating metadata for 11 gems ....

I justed typed "gem outdated" and got the following output in my terminal:

Updating metadata for 11 gems from http://gems.rubyforge.org

My first thought was that there are some gems neeeded to be updated - so I
typed it again and got the following:

bullet:~ root# gem outdated
bullet:~ root#

So there are no updates available.
What exactly does "Updating metadata for 11 gems..." mean?