'Shū yún' (书云) is a classical Chinese literary phrase meaning 'as the book says' or 'according to the text.' It originates from formal, scholarly, or historical writing and functions as a citation marker—similar to English expressions like 'as stated in the records' or 'the text states.' The character 书 (shū) means 'book,' 'text,' or 'written record,' while 云 (yún) is an archaic verb meaning 'to say' or 'to state,' often used in classical texts to introduce quotations.

This phrase is rarely used in modern spoken Chinese but appears in academic writing, historical commentary, classical literature translations, and formal essays when referencing authoritative sources. It conveys respect for textual authority and scholarly tradition. Learners will encounter it primarily in reading classical or semi-formal texts—not in everyday conversation—and should recognize it as a set phrase rather than a literal combination of its characters.