ORIGINAL: DBCherry
What Chevelle said. Except, washout is when the underside of the wing's trailing edge, at the last few bays, sweeps upward slightly in relation to the inner trailing edge. By adding washout, the air slips out from under the outer edge of the wing more quickly than the inner trailing edge, and that helps reduce tip stalls.
Dennis-
I know you know exactly what you are saying, and you are right, but I have an "easier to understand" explaination of washout.
Three factors are critical for wing stalls... Airspeed, angle-of-attack, and proximity to the wing tip (because air can "wrap around" the wingtip disrupting laminar flow). Thus the wing-tips are more vulnerable to stalling than the wing root.
Washout decreases the angle-of-attack of the wing tip relative to the rest of the wing, reducing it's vulnerablility to stall.
gus