A dressing area/anteroom to the bathroom — a place to undress or change (in baths, homes, etc.).
銭湯の脱衣所でロッカーに着替えを入れた。
I put my change of clothes in the locker in the bathhouse dressing room.
入浴前に脱衣所で体を洗っておこう。
I'll wash up in the dressing area before taking a bath.
A changing room (at a bathhouse, swimming pool, etc.).
プールの脱衣所は混んでいたので、少し待った。
The pool changing room was crowded, so I waited a bit.
病院の脱衣所で検査着に着替える。
Change into an exam gown in the hospital changing room.