IFR is instrument flight rules, rules for when flight by outside visual reference is not safe.
IFR may also refer to: Infection fatality rate in epidemiology Ideal final result, an engineering design goal In-flight refueling Institute of Food Research, an agricultural and food science research institution Integral fast reactor, a nuclear reactor design International Federation of Robotics International Financing Review, a financial magazine International Fleet Review, various publications of the same name Instantaneous wave-free ratio (iFR), a diagnostic medical test used in coronary artery stenosis assessment Immortals Fenyx Rising, a 2020 video game Infield fly rule, a rule in baseball that treats certain balls as caught regardless of outcome