I also host game jams from time to time! What's a game jam? Well, a game jam is basically an event where participants try to make a video game from scratch. -Wikipedia.

Most of the time, there will be a theme and/or common limitation/rule for participants to follow. (E.g. B&W Jam - only uses the color black and white, a jam about time. - implement a game mechanic which makes creative use of the properties of time)