A swimsuit or bathing suit—garments worn for swimming at pools or the beach.
夏休みに新しい水着を買った。
I bought a new swimsuit for summer vacation.
海では水着に着替えて泳いだ。
At the beach I changed into a swimsuit and swam.
プールでは必ず水着の着用が必要だ。
Wearing a swimsuit is always required at the pool.