Refers to the absorbent material used for cleaning, bathing, or as a tool. Also used in compound words like スポンジケーキ (sponge cake).
食器を洗うときはスポンジを使います。
I use a sponge when washing dishes.
Please wipe the table with a sponge.
I washed the dishes with a sponge.
I wrung out the used sponge well before putting it away.
This cake is soft like a sponge.