上任 (shàng rèn) is a verb meaning 'to take office' and a noun meaning 'predecessor'. As a verb, it is more formal than 就职 (jiù zhí) and 就任 (jiù rèn), often used for high-level appointments. As a noun, it specifically means the person who held the position immediately before you, unlike 前任 (qián rèn) which can also mean an ex-spouse, or 前辈 (qián bèi) which refers to a senior or elder in a field.