Things that need to be washed — especially dishes and cooking utensils (or, less commonly, laundry).
朝ごはんの後で洗い物をした。
I did the dishes after breakfast.
パーティーの後は洗い物がたくさんある。
There are a lot of dishes to wash after the party.
母が『洗い物は私がやる』と言ってくれた。
My mother said, 'I'll do the washing up.'