Plain English Meaning
The amount you turn the nose of the airplane into the wind so that the airplane actually moves across the ground in the direction you want, instead of getting blown off course.
Full Definition
The angle between an aircraft's heading and its desired course, applied to compensate for the effect of wind so that the aircraft tracks the intended path over the ground.
Context Anchor
Used in navigation planning, cross-country flying, and any time wind would push the airplane sideways from the planned route.
Derivation
A plain combination of three everyday words. 'Correction' here means an adjustment to a problem -- in this case, the problem of wind pushing the aircraft sideways. The whole phrase describes exactly what it does: the angle you add to correct for wind.