1 or more single dollar bills placed between dollar bills of a larger denomination (like 20's, 50's, or Benjamins). Used to hide the larger bills, in order to fool people into thinking you have less money than you actually have.
Guy 1: I was opening my wallet today to get out my train ticket, when a hobo walked around begging for money.
Guy 2: Oh, man. He didn't get a 20 out of you, did he?
Guy 1: Nah, thankfully he only saw my buffer singles. All he got was 1 dollar.