Plain English Meaning

Your eyes give you the wrong picture. What you think you see — how high you are, how far away the runway is, whether the wings are level — is not what is actually happening.

Full Definition

A misleading visual impression in which what the pilot sees does not match the actual situation, often producing incorrect judgments of altitude, distance, attitude, or motion. Common in flight when normal visual references are reduced, distorted, or absent — for example at night, in haze, over featureless terrain, or on approach to runways of unusual size or slope.