粗鲁 (cū lǔ) is an adjective meaning 'rude' or 'impolite', describing behavior that lacks basic courtesy, social awareness, or respect for others. The first character 粗 (cū) literally means 'coarse', 'rough', or 'crude', suggesting something unrefined or lacking subtlety; the second character 鲁 (lǔ) originally refers to the ancient state of Lu but in modern usage carries connotations of 'clumsy', 'naïve', or 'socially inept'. Together, they evoke a sense of behavioral coarseness — speaking bluntly without tact, interrupting, ignoring social norms, or acting inconsiderately.

This word is commonly used in everyday criticism or advice, especially when addressing inappropriate conduct in personal, workplace, or educational settings. It’s stronger than terms like 不礼貌 (bù lǐmào, 'impolite') and often implies a deeper lack of self-awareness or empathy. While not extremely formal, it’s appropriate in neutral-to-serious contexts — you might hear a teacher say it to a student or a parent correcting a child. It’s rarely used as a noun or verb; its primary function is adjectival.