1.
one's specialty, forte, go-to
Something a person is especially good at or known for, often a signature skill, dish, song, or trick.
カレーは母の十八番だ。
Curry is my mother's specialty.
カラオケでの十八番は何ですか。
What's your go-to song at karaoke?
遅刻の言い訳は彼の十八番で、毎回違う理由を考えてくる。
Making excuses for being late is his specialty — he comes up with a different reason every time.
READING:
The reading おはこ is irregular. The kanji 十八番 can also be read じゅうはちばん, which is used more formally or in kabuki contexts.
ETYMOLOGY:
From kabuki theater. The Ichikawa family stored their eighteen best plays in a special box (箱), and these came to be called 十八番. The お is an honorific prefix.
USAGE:
Used casually to refer to someone's best skill, go-to karaoke song, signature dish, or any recurring behavior (sometimes humorous). The pattern ～は十八番だ is standard.