已知 literally means 'already known' — 已 (yǐ) means 'already' or 'by now', and 知 (zhī) means 'to know' or 'knowledge'. Together, they form an adjective describing information, facts, conditions, or values that are already established, given, or confirmed in a context — especially common in academic, technical, mathematical, or logical discussions. It often appears before nouns (e.g., 已知条件 'given condition', 已知事实 'established fact') and functions similarly to English adjectives like 'known' or 'given'.

This term carries a formal, objective tone and is rarely used in casual speech. You’ll frequently encounter it in textbooks, scientific writing, problem-solving scenarios (like math word problems), or news reports citing verified data. It contrasts with 未知 (wèi zhī, 'unknown') and emphasizes reliability or prior confirmation rather than personal awareness.