Well, I am back from the drum circle now, so I will tell you.
It is a gathering where people get together and play drums. Sometimes people will also play digeridoos, rattles, shakers, recorders, etc as well. Normally the players form a circle so that everyone can see everyone else. Most of the drums are hand drums, played without drumsticks, by hitting them with your hand.
Most, though not necessarily all of the drums are of an African style called djembe, pronounced gem-bay. There are also African drums called boogeraboos (not sure of the spelling), and doondoons (?spelling again). Then there are a couple of Middle Eastern styles called doombeks, and tablas. Let's not forget the good ol' bongos, congas, baliphones, and several others that I don't know the name of.
Now.... are you sorry you asked?
Drum circles can run the gamut from crazy jam sessions with everybody playing different rhythms, to very structured affairs with something akin to a director calling in certain drummers at particular times to play their individual parts. The two different ones that myself and my son go to are somewhere in between, with a rhythm being agreed upon, but everyone is free to play whatever they want that still fits with that rhythm. The one we went to tonight is a very family oriented situation, with little kids running around and such.