change of clothes; spare clothing
Refers to a set of clothes brought along to change into, such as after exercise or for an overnight stay.
Don't forget a change of clothes for the trip.
ジムのロッカーに替え着を入れておく。
I keep a change of clothes in my gym locker.
Compound of 替え (change, substitute) and 着 (clothing). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning.