The Japanese go term aji keshi, which has been adopted into English, consists of the terms aji (possibility) and keshi (erase). Aji keshi is a move that unnecessarily removes one's own good aji in the opponent's position and an important concept to understand.
Even an elementary peep () can be an aji-keshi...
...because Black has another possibility of playing a wedge and cut somehow, which may be more damaging to White depending on circumstances.
Often seen aji-keshi in amateur games is an automatic atari like . He must defend at .