Plain English Meaning
A constant pattern of looking from one instrument to another so the pilot always has an up-to-date picture of how the aircraft is flying, instead of staring at just one gauge.
Full Definition
The systematic, continuous scanning of flight instruments by the pilot to detect deviations from desired flight conditions and verify the aircraft's attitude, performance, and trajectory. The technique involves shifting visual attention between instruments in a deliberate pattern rather than fixating on any single indicator.