二十 (èr shí) is the Chinese numeral for 'twenty'. It literally combines the characters 二 (èr), meaning 'two', and 十 (shí), meaning 'ten' — together forming 'two tens', or 2 × 10 = 20. Like all Chinese numerals, it functions as a determiner before nouns (e.g., 二十本书) or as a standalone number in counting, age, time, and measurement contexts.

This word follows standard Chinese numeral formation: multiples of ten are expressed as [digit] + 十, so 二十, 三十, 四十, etc. Unlike English, Chinese does not use a separate word like 'twenty'; instead, it builds numbers transparently from basic digits and place values. It’s used frequently in daily life — stating ages, prices, quantities, dates, and time (e.g., 二十点 for 8 p.m.). Note that it never takes measure words on its own; a measure word is required when modifying a noun (e.g., 二十个苹果, not *二十苹果).