‘小妹’ literally combines ‘xiǎo’ (small, young) and ‘mèi’ (younger sister), so its core meaning is ‘youngest sister’ — the youngest female sibling in a family. It emphasizes relative age and familial position, not just birth order but also a sense of youthfulness and closeness.

Importantly, ‘xiǎo mèi’ is also widely used by young or middle-aged women as a humble self-reference in informal or service contexts — for example, when speaking to elders, customers, or strangers — to convey modesty and politeness. Unlike formal pronouns like ‘wǒ’, it softens the speaker’s presence and signals deference or warmth. This usage is common in spoken Mandarin but rarely appears in formal writing.