预防 means 'to prevent'—specifically by taking proactive measures before something harmful or undesirable occurs. The character 预 (yù) means 'in advance' or 'beforehand', while 防 (fáng) means 'to guard against' or 'to defend'. Together, they emphasize foresight and preparation rather than reactive action. This word is commonly used in contexts involving health, safety, environmental protection, and risk management.

You’ll frequently encounter 预防 in public health messaging (e.g., disease prevention), workplace safety guidelines, and educational materials about healthy habits. It’s a formal, standard term—not slang—and appears in both written and spoken Mandarin, especially in official, medical, or technical discourse. Unlike the more general verb 防止 (to prevent/stop), 预防 highlights the timing: it stresses acting early, before the problem arises.