Definition of "FIR"

(signal processing, of a filter) Initialism of finite impulse response; that has impulse response (or response to any finite length input) of finite duration.  examples

(aviation) Initialism of flight information region; a specified region of airspace in which a flight information service (FIS) and an alerting service (ALRS) are provided  examples

(South Asia, Singapore, law enforcement) Initialism of first information report.  examples

(uncountable) Abbreviation of far infrared or far infrared radiation.  examples