Leg-yield
The leg-yield is a lateral movement in which a horse travels both forward and sideways at the same time. The horse is fairly straight through his body in the leg-yield, although he may have a slight bend opposite to the direction of travel. It is one of the "three initial movements leading up to true lateral work", the others being the turn on the forehand and the shoulder-fore.
Difference between the leg-yield and half-pass
The leg-yield and half-pass are sometimes confused because they are both movements in which the horse goes forward and sideways. However, the half-pass is quite a bit more advanced, requiring greater balance, engagement, and collection from the horse. In the leg-yield, the horse is fairly straight or bent slightly away from the direction of travel. In the half-pass, the horse is bent towards the direction of travel, which is physically much more difficult for the horse.
Uses and disadvantages of the leg-yield
The leg-yield is one of the first lateral exercises to be introduced to a horse, teaching it a simple yet valuable lesson: to move sideways away from leg pressure. This basic is later built upon in the shoulder-in and haunches-in.