Washout is the design of the aircraft wing with the slight twist reducing the angle of incidence from the root to the tip. In this type of design root will have the higher angle of coincidence than the tip of the wing. This is to make sure that at the any given point of time, the root of the wing will fly at the higher angle of attack than the tip of the wing. This will make the root of the wing to attain the critical angle of attack than the tip and stall first. This will allow the enough airflow over the tips to prevent any rolling motion during the stall.