How do you describe what "Doh" means?

One of my co-workers found the cause of a particularly nasty bug to be a simple fix. When he showed me, in my IM client, I replied "Doh!"

His very appropriate response was "doh means?"

How do you describe the meaning of "Doh"? It's not in the dictionary (or is it?).

In fact the best way to describe it is to actually watch the Simpsons.

I pointed him to the link above and ran off to a meeting.