Instrument meteorological conditions (
IMC) is an
aviation flight category that describes weather conditions that require pilots to fly primarily by reference to instruments, and therefore under
instrument flight rules (IFR), rather than by outside visual references under
visual flight rules (VFR). Typically, this means flying in
cloud or bad
weather. Pilots sometimes train to fly in these conditions with the aid of products like
Foggles, specialized glasses that restrict outside vision, forcing the student to rely on instrument indications only.