'里面' (lǐ miàn) literally combines '里' (lǐ), meaning 'inside' or 'within', and '面' (miàn), meaning 'surface' or 'side'. Together, they form a compound that means 'inside' or 'indoors' — referring to the interior space of something physical, like a room, container, or building. It functions as both a noun ('the inside') and an adverb ('inside [somewhere]').

It’s commonly used after location words (e.g., 房间里面, 盒子里面) or with verbs of motion or position (e.g., 进去、在、坐). Unlike the standalone character '里', which can mean 'village' or be a measure word, '里面' is strictly spatial and never used for abstract 'interior' in formal or metaphorical senses (e.g., not for 'inner feelings'). It’s neutral in register and widely used in daily speech and writing.