Plain English Meaning

The propeller throws a twisting column of air backward over the airplane. That spinning air hits the tail from one side and pushes the nose to the left, especially when power is high and the airplane is moving slowly.

Full Definition

The yawing and rolling tendency caused by the spiraling slipstream from the propeller striking the left side of the vertical stabilizer (in most U.S.-built single-engine aircraft, where the propeller rotates clockwise as seen from the cockpit). This sideways push on the tail produces a left-yawing moment, most pronounced at high power settings and low airspeeds.