‘外甥’ (wài shēng) means ‘sister’s son’—specifically, the son of one’s sister. It is a kinship term used exclusively for male relatives on the maternal side. The first character, 外 (wài), literally means ‘outside’ or ‘external’, reflecting the traditional Chinese kinship system where siblings’ children are considered ‘outside’ the direct paternal line. The second character, 甥 (shēng), historically denotes a nephew (maternal or sometimes paternal), but in modern standard Mandarin, it only appears in compound terms like 外甥 (maternal nephew) and 外甥女 (maternal niece). Together, 外甥 emphasizes the maternal lineage and distinguishes this relationship from 姪子 (zhí zǐ), which refers to a brother’s son.

This term is used in both formal and informal contexts, especially when specifying family relationships in conversation, documents, or introductions. It carries no special formality or informality—it’s neutral and widely understood across regions. While ‘nephew’ in English covers both maternal and paternal nephews, Chinese makes a clear distinction: 外甥 is strictly maternal, and 姪子 is strictly paternal. Confusing the two is a common error among learners.