A small, bright object, usually hand-held, and as such, not to be confused with TheMoon (although they are both frequently seen at night). Useful for emergency lighting and/or generally looking cool. Also seen at ItrGames at the Wash.
If thrown high enough, a really bright one of these might be used as a SignalFlare.
Also cool are the non-hand-held variety which are small and mouth-held. If they break they're really bitter (at least the blue ones...maybe the green ones are a different flavor) and it makes your spit glow for a little bit.
Very useful during Power Outages.