A phrase used to signify that a game of "street dice" is about to begin shortly. Since street gambling is illegal, the phrase "money on the floor" is a way to quickly and covertly gather people to begin gambling.
The person ready to initiate the gambling will have often have dice-in-hand and will throw down the amount of money he is willing to bet onto the floor. At this point he will scream at the top of his lungs "money on the floor!" At this point, potential gamblers will approach and will decide whether or not to match the wager. If a potential gambler would like to match the wager, he will throw down a matching amount and will scream back "money on the floor!" At this point, the dice gambling will begin.
Should a prospective gambler refuse to match any bets in a dice game, he will be barred from ever starting a "money on the floor" holler in the future.
Person One: Bro, did you hear about Thomas?
Person Two: No. What happened?
Person One: He works at Mcdonald's now because he was always throwing his "money on the floor"
Person Two: No worries. He's in a rough patch now and will soon be back on top of the dice game.