The age at which one is finally considered human.

To '21' something is to quit it, to give up on something.

The magical age where it is legally ok to get incredibly drunk. At this time, a young adult spends most of his free time consuming vast amounts of alcohol in a variety of forms, saying that they're "making up for lost years."

The magic number in the game of Blackjack.

The legal drinking age in the United States.

After Prohibition, the age was usually 18 depending on the state, but then in the 1980s President Reagan created a highway subsidy program which basically bribed the states under the condition that the drinking age was raised to 21.

As a result, immaturity, irresponsibility, partying, DUI, and bar attendance increased by an additional 3 years, which continues to this day.

When you compare America to European countries which don't have a legal drinking age, you realize that this behavior is irreversible in the short term and thus no politician will ever lower the drinking age back to 18. Except the Libertarian Party or maybe Ron Paul.

Basketball games where everyone is scoring on their own part, and not for a team. The object of the game is to get exactly 21 points, not under, or over. The game can go by extremely slow or extremely fast depending on who you're playing against and what rules you're using.

The break is the opening shot that a person calls to take and is worth three points. He will shoot this shot from either the three point or free throw line with no one guarding him. The ball goes into play as soon as it is released from his fingetrips.

Some extra rules that people like to play with to make the game more fun include tipping, tip zones, street ball, and poison.

Tipping is when one player shoots the ball in an attempt to score. The shooter must have missed the shot and another, opposing, player catches the ball in mid-air while his feet are off the ground and makes the shot which the other player missed. When this has happened, the player who made the basket sends the person who originally shot the ball back down to 13, 0, or out of the game (depending on what that player has and what rules you're playing by).

Tip zones are basically the amount of points you have when you were tipped. If you had above 13 points when you were tipped, then you would be sent back down to 13. If you had 13 or less points when you were tipped, you would be sent down to zero. (Optional Rule) If you had zero when you got tipped, you would be eliminated from the game until it ended. The rul...

The REAL age of majority according to most people, though I don't think people act and look like adults until their mid-twenties. I'm 19 and I don't consider ANYONE at my college an "adult".