The act of waiting or the waiting time/state; a noun used widely in everyday contexts.
彼からの連絡待ちで落ち着かない。
I'm restless waiting for his message.
駅の待ちは混んでいて座れなかった。
The line at the station was crowded and I couldn't sit while waiting.
待ち時間はおよそ30分です。
The waiting time is about 30 minutes.
In mahjong, the tile(s) that complete a hand (the waiting tile). Examples include ryanmen-machi (two-sided wait), tanki-machi (single tile wait), etc.
あの手は両面待ちだからツモ率が高い。
That hand is a two-sided wait, so the chance of drawing the winning tile is high.
単騎待ちより両面待ちの方が安定している。
A one-tile wait is less stable than a two-sided wait.
今の形は三面待ちになっている。
The current shape is a three-sided wait.