bad move; poor play
Primarily used in board games like chess and shogi to describe a move that worsens one's position. Can also be used metaphorically for a poor decision in other contexts.
That bad move suddenly turned the position unfavorable.
He made a bad move in the endgame and lost by a reversal.
悪手 is a bad or losing move in shogi/go, the direct opposite of 妙手's brilliant move.
Compound of 悪 (bad) and 手 (move, play). The reading あくしゅ follows standard on'yomi.