expression, ichidan verb
be off-pitch; be off-key; be out of tune
Describes singing or playing an instrument where the pitch is not accurate. The phrase is a set expression using 音程 (pitch) and 外れる (to deviate).
彼は歌うとよく音程が外れる。
He often goes off-pitch when he sings.
このギターは音程が外れているから、チューニングが必
This guitar is out of tune, so it needs tuning.