Definition
A set of FAA regulations governing the conduct of flight in instrument meteorological conditions, or any flight operating on an IFR flight plan, where the pilot navigates and controls the aircraft primarily by reference to cockpit instruments rather than visual reference to the ground or horizon. IFR operations require an IFR flight plan, an ATC clearance, and pilot and aircraft qualifications appropriate to instrument flight.
Plain English
The rules pilots fly under when they can't rely on seeing outside -- such as in clouds or low visibility -- and must instead fly by their instruments while following directions from air traffic control.
Context Anchor
You will see IFR on flight plans, clearances, weather discussions, approach procedures, and in phrases such as “IFR conditions” or “cancel IFR.”
Derivation
From the words 'Instrument' (the cockpit gauges and displays the pilot uses to fly), 'Flight,' and 'Rules' (the regulations governing how that flight is conducted). Named to contrast with VFR -- Visual Flight Rules -- where the pilot relies on outside visual reference.
Why Pilots Care
Determines required pilot training, aircraft equipment, and separation standards that keep flights safe when visibility is limited.
Intuition Check
IFR does not simply mean “bad weather.” A flight can operate IFR in clear weather, and bad weather may require IFR procedures if the pilot cannot safely fly by outside visual reference alone.
Example Sentence 1
We filed IFR for the trip because a low ceiling was forecast at our destination.
Example Sentence 2
ATC issued an IFR clearance that included a specific altitude and route to the destination airport.