Definition of sideslip:
(n) :
(aviation) A flight manoeuvre that uses opposing rudder and aileron inputs to move the aircraft sideways without turning it.
(n) :
(aviation) A flight maneuver to rapidly lose speed and/or altitude whilst not altering the aircraft's ground track.
(n) :
(aviation) A flight condition where an aircraft's longitudinal axis is not aligned with its direction of motion relative to the surrounding air.
(n) :
(aviation, uncountable, by extension) The angle between an aircraft's longitudinal axis and its direction of motion relative to the surrounding air.
(v) :
(aviation) To perform, or place an aircraft in, a sideslip.