Definition
A flight condition in which the airplane's longitudinal axis is not aligned with the relative wind, causing the aircraft to move partly sideways through the air. In a sideslip, the aircraft's heading and flight path differ, with the nose pointed away from the direction of travel. It is intentionally produced by applying opposite aileron and rudder, so that the bank in one direction is balanced by yaw in the other.
Plain English
A controlled maneuver where the airplane flies slightly sideways through the air, with one wing lowered and the nose held off to the opposite side using the rudder.
Context Anchor
Seen in discussions of uncoordinated flight, stalls and spins, and crosswind landings.
Derivation
From 'side' (lateral direction) plus 'slip' (to slide). The word captures the idea of the airplane sliding sideways through the air rather than tracking straight ahead along its nose.
Why Pilots Care
Used to lose altitude without gaining speed or to counteract drift from a crosswind while keeping the airplane pointed down the runway.
Intuition Check
Do not think of a sideslip as the airplane slipping on the ground or simply losing altitude. In flight, it means the airplane has a sideways motion through the air.
Example Sentence 1
The pilot used a sideslip on final approach to stay aligned with the runway centerline in the crosswind.
Example Sentence 2
In spin awareness practice the instructor demonstrated how an uncorrected sideslip can allow one wing to stall first and start autorotation.