simple recursion help

[Steven Bethard]

drs <drs <at> remove-to-send-mail-ecpsoftware.com> writes:
> 
> I am looking for a list of all unique strings of length x whose
> elements are from the set a, b, and c.

Does anyone know what this operation is called?  It's not permutations or
combinations as I understand them since permutations and combinations do not
allow repetition.  I assume there was already a solution for this somewhere, but
I didn't know what term to google for.

Thanks,

Steve