自燃 (zì rán) literally means 'self-ignite' — 自 (zì) means 'self' or 'by itself', and 燃 (rán) means 'to burn' or 'to ignite'. Together, they form a scientific term meaning 'spontaneous combustion': the process by which a substance catches fire without an external ignition source, typically due to internal heat buildup from chemical reactions like oxidation.

This word is used primarily in technical, safety, or medical contexts — for example, when discussing industrial hazards (e.g., oily rags self-igniting), chemical storage protocols, or rare medical cases where body tissues are metaphorically described as undergoing 'self-ignition' (though this usage is highly figurative and uncommon). It is not used for everyday fires or cooking. The term carries a formal, precise tone and appears in news reports about warehouse fires, safety manuals, and chemistry textbooks.