Not all slot machines are created equal. In the early days, slot machines were totally unpredictable. Each spin of the three reels was independent of other spins, making their stops completely random. Today's machines are programmed. Each casino must pay out a percentage of what ever they take in each and every day.
Loose machines are ones which pay back a higher percentage of what they take in.
Loose slot machines are the ones that pay out a higher percentage of what they take in. These are the machines you want to play. These loose machines can actually pay out more coins in a day's time then they take in. Loose machines must do this to make up for the very tight machine. Blackjack is a very popular game because its the only game in which the odds of winning are really under YOUR control.