The point in which a runner on a long-distance run has been drained of energy and his or her body seizes up. Very painful, very difficult to get passed.

The point at which a girl that used to be hot, is no longer hot. This is typically due to advancing age.

when a girl becomes officially ugly

when you reach a point of total exhaustion or fatigue.

To 'hit the wall' is to suddenly reach a mental block. It could be as simple as running out of ideas or as complex as not knowing what to do in life. Hitting the wall usually happens suddenly and the effects can last for long periods of time.

Slang for when you run out of energy / calories when exercising.

The point you get to when you can't drink any more booze or smoke any more dope and just need to pass out.