There have been many ways to describe a common office phenomenon. Some call it a gift, others litter, but I think most apt is "Found Cake." To understand this definition, please refer to the following web comic.
Penny Arcade - It Looks Delicious
Now, coming across "found cake" on the street is one thing. I'm not sure how interested I would be in picking up that treat. In an office though, it's a treat. No one knows exactly where it comes from, they only know they got there just in time.
In fact if I'm not mistaken, there's an economic theory that the utility derived from "found cake" is inversely proportional to the amount left after you have taken your piece. In layman's terms, if you're the last person to get a piece, you ultimately end up enjoying it the most. I find this is true regardless of the size of the piece you do end up getting. Mostly because if you get the last piece, you also get the implied right to gloat to others about your feat. It's just polite.
I wonder if any "found cake" studies have been performed. I bet you they'll find that the first slice is the largest and the last slice lasts the longest. Maybe that's what we were just subjected to, a "Found Cake Study." I think in either case, it is a win / win. Free cake in the name of science. Keep the found cake coming.