凡例 (fán lì) is a formal noun referring to the explanatory preface or key found at the beginning of reference books, dictionaries, atlases, or academic publications. It outlines the conventions, symbols, abbreviations, formatting rules, and editorial principles used throughout the work — for example, explaining what ‘→’ means, how entries are ordered, or how pronunciation is indicated. The character 凡 (fán) means ‘all’ or ‘general’, suggesting comprehensiveness, while 例 (lì) means ‘example’, ‘precedent’, or ‘case’; together, they convey the idea of ‘general examples’ or ‘standard conventions’ that apply across the entire text.

This term appears almost exclusively in printed or digital reference materials — not in everyday speech or casual writing. It’s commonly placed right after the title page and before the main content, often titled ‘凡例’ in bold or as a section heading. Readers consult it to understand how to interpret the book’s structure and notation correctly, making it essential for effective use of technical or scholarly resources.