"Fā rè" literally combines "fā" (to emit, to develop) and "rè" (heat), meaning 'to run a fever'—a common symptom of illness where body temperature rises abnormally. It is used almost exclusively in medical or health-related contexts to describe human physiological responses, especially during infections like colds or flu. Unlike general terms for 'heating up,' this phrase carries clinical connotation and implies discomfort or illness.

The word functions as an intransitive verb and typically appears in simple subject–predicate structures: e.g., 'tā fā rè le' (he/she has a fever). It can also appear in compound phrases like 'fā rè chōngxuè' (fever with congestion) or 'fā rè yǐnqǐ de tóutòng' (headache caused by fever). While occasionally used metaphorically for machines overheating, such usage is rare and often marked as figurative or humorous in everyday speech.