instrument meteorological conditions

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.