入口 (rù kǒu) literally combines 入 (rù), meaning 'to enter', and 口 (kǒu), meaning 'mouth' or 'opening'. Together, they form a compound noun meaning 'entrance'—a physical point of entry into a space, such as a building, park, subway station, or even a website interface. It emphasizes the functional role of the opening as a gateway rather than just its shape or size.

This word is commonly used in urban, architectural, and digital contexts—for example, on signs ('入口' indicates where to go in), in directions ('从东入口进入'), or in computing ('登录入口' means 'login entrance'). Unlike the more poetic or literary 门口 (ménkǒu, 'doorway') or formal 大门 (dàmén, 'main gate'), 入口 is neutral, practical, and widely understood in both spoken and written modern Chinese.