‘杯子’ (bēi zi) is a common noun meaning 'cup'—a small, handheld container used for drinking liquids like water, tea, coffee, or juice. The first character 杯 (bēi) by itself means 'cup' and carries the core meaning; the second character 子 (zi) is a diminutive or nominal suffix that makes the word more colloquial and concrete, typical of many everyday nouns in Mandarin (e.g., 桌子 zhuōzi 'table', 筷子 kuàizi 'chopsticks'). Unlike formal or literary terms, 杯子 is neutral in register and used widely in daily conversation, at home, in offices, and in restaurants.

This word refers specifically to reusable, open-topped drinking vessels—usually made of glass, ceramic, plastic, or metal—and excludes disposable paper cups (which are often called 纸杯 zhǐ bēi) or mugs (which may be called 马克杯 mǎkè bēi). It’s countable and commonly paired with measure words like 个 (gè), as in 一个杯子 (yī gè bēi zi). While 杯 can appear alone in compound words (e.g., 一杯水 yī bēi shuǐ 'a cup of water'), 杯子 emphasizes the physical object itself.