Youth slang.
Entering a store today, I was accosted by an apparently misguided youth. He ran up to me and, wild-eyed, asked, “Got a square?” I replied in the negative, presuming the subject was illicit in nature. That was not technically correct. According to the useful Urban Dictionary (*) that I later discovered, I was able to learn that he was speaking of a cigarette. I was right in denying him. As always, I have no square.