This is a method of dealing cards by flicking them off the deck with one hand. The hand position necessary for to perform the flourish is very similar to the natural dealing position, so it's easy to flick off a couple cards in the middle of your deal.
Maybe you only have the one hand. Maybe you want to show off. Maybe you're just too cool to deal cards with both hands. Whatever the reason, this is a skill that will elevate your status from card player to master card manipulator. Okay, maybe not. Still, it's fun to do.
(See the youtube video clip