Toe-out on turns is the relative toe setting of the front wheels, as they turn to left, or right.
When a vehicle makes a turn, each wheel should rotate with true rolling motion, that is free from tire scrub.
True rolling motion is only obtained when each wheel is at 90 degrees to a line drawn between the swivel axis and the center of turn.
Because the rear wheels are fixed, the center of turn will lie somewhere along the centerline of the rear axle, depending on how far the steering wheel is turned from the straight-ahead position.
To provide true rolling motion, the inner wheel must be turned through a greater angle than the outer wheel. This allows the inner wheel to turn through a smaller turning radius than the outer wheel.
This automatically correct alignment is obtained by use of the Ackerman principle and layout. With the steering linkage at the rear of the wheels, the distance across the tie-rod ends, at the steering arm joints, is made shorter than the distance across the steering axis swivels. This forces the inner wheel to turn through a larger angle when the steering is turned.
The Ackerman angle is the angle the steering arms make with the swivels, on the centerline of the vehicle, at or near the center of the rear axle.