第二 (dì èr) is the Chinese ordinal numeral meaning 'second'—used to indicate position or sequence in a series, such as 'the second person', 'the second floor', or 'the second time'. It consists of two characters: 第 (dì), a prefix that marks ordinal numbers (like English 'the ___-th'), and 二 (èr), the cardinal number 'two'. Unlike English, Chinese ordinals always require 第 before the cardinal number; you cannot say *二 alone to mean 'second'.

This word appears frequently in daily contexts: ranking (e.g., 第二名), time sequences (e.g., 第二节课 'second class period'), location (e.g., 第二层楼 'second floor'), and repetition (e.g., 第二次 'second time'). It’s neutral in register—used in both spoken and written Chinese—and pairs naturally with measure words and nouns. Note that 第二 is not used for fractions or decimals; it strictly expresses order, never quantity.