Slip-ons are shoes with no fastening: you slide your feet in and walk. People almost always say the plural, because shoes come in pairs — “Where are my slip-ons?” — even though the singular slip-on also exists. Same idea as slip-on shoes: no laces, no buckles, no zips. They are not house slippers, though both are easy to put on. Everyday shop and clothing talk; slightly informal, completely normal.

懶人鞋；套穿鞋。英語裡常講複數 slip-ons，因為鞋子成雙。