Plain English Meaning

Weather that is too poor to fly by looking outside. The clouds are too low or visibility is too limited, so the flight has to be conducted using instruments and under air traffic control.

Full Definition

Weather conditions below the minimum visibility and cloud clearance values prescribed for visual flight. When IFR conditions exist, flight is permitted only under Instrument Flight Rules, which require an instrument rating, an IFR flight plan, and an ATC clearance.

Context Anchor

Seen in weather reports, flight planning, pilot briefings, and discussions about whether a flight can be made under rules or must be conducted under rules.