Plain English Meaning

The wing stops producing lift at its tips before it stops at the part nearest the fuselage. On swept wings this is dangerous because losing lift at the tips makes the nose pitch up, which makes the stall worse instead of letting the aircraft recover.

Full Definition

A stall that begins at the outer end of the wing rather than at the wing root. On swept-wing aircraft, spanwise airflow toward the tips causes the boundary layer to thicken outboard, so the tips lose lift first as the angle of attack increases. Because the tips are aft of the aircraft's center of gravity on a swept wing, a wingtip stall shifts the remaining lift forward, pitching the nose up and deepening the stall.