noun
chest hair; breast down
Refers to hair growing on the chest, typically of men. 'Breast down' is a less common, more literary or poetic term.
彼は胸毛が濃い。
He has thick chest hair.
胸毛を剃る男性もいる。
Some men shave their chest hair.
Compound of 胸 (chest) and 毛 (hair).