Plain English Meaning

A side slip is when the pilot deliberately banks the wings one way and pushes the rudder the other way, so the airplane keeps flying straight ahead but slides slightly sideways through the air. It is used to lose altitude quickly or to stay lined up with the runway in a crosswind.

Full Definition

A controlled flight maneuver in which the airplane's longitudinal axis remains aligned with the original flight path, but the airplane is banked into the wind while opposite rudder is applied to prevent turning. The result is a flight path that tracks straight ahead while the airplane moves sideways through the air, increasing drag and steepening the descent without increasing .