Tiny pieces, flakes or perhaps even buds of Marijuana, which fall out of pipes, bowls, and carelessly closed plastic baggies into the coat pocket during transport.
In civilized countries coat weed can inhabit coat pockets for several weeks during winter season in cold climates. Coat weed can be harvested and smoked during times of need, however it is not recommended that one share this harvest with others (esp. the opposite sex) as you could be mistaken for being desperate to get high, broke or just downright pathetic.
Bob: "Hey Doug you got any weed eh?"
Doug: "Take off! All's I've got's a bowl a' coat weed."
Bob: "Coat weed? Aw that's lame you hoser! Take Off!"