快乐 (kuàilè) is a common two-character adjective meaning 'happy' or 'joyful'. It combines 快 (kuài), which conveys speed, lightness, or ease, and 乐 (lè), meaning 'pleasure' or 'delight'. Together, they evoke a sense of spontaneous, unburdened joy — not just momentary cheerfulness, but a deeper, warm emotional state. It’s widely used in both spoken and written Chinese to describe people’s feelings, experiences, or environments.

This word often appears in everyday expressions like '祝你快乐' (Wishing you happiness), in literature, songs, and formal contexts such as speeches or greeting cards. Unlike the more casual 愉快 (yúkuài) or the stronger 兴奋 (xīngfèn), 快乐 emphasizes enduring, wholesome happiness — think of childhood joy, family gatherings, or peaceful contentment. It can modify nouns (e.g., 快乐的时光 'a happy time') or follow verbs like 是 or 感到 ('feel happy').