The term “sway” in a golf swing can carry a lot of meaning, both good and bad. First, to define sway, we are normally speaking about lateral shift of the body in the backswing (only). To take it a step further, we generally assess “sway” in two body segments: the pelvis (lower body) and the torso (upper body). Think of your belt buckle as the pelvis and your shirt buttons as your torso.
It’s important to note that we can look at each segment individually. For a right-handed golfer for example, the pelvis can sway to the right in the backswing, while the torso might remain stable. Or, the torso can sway to the right, while the pelvis remains stable. Or, both segments could sway rightward together! Looking at each part of the body individually helps us as teachers best identify a player’s movements and how we can increase their efficiency. Finding a quality coach can help you identify your specific tendencies and evaluate if there is room for improvement.
In general, though, swaying of the torso and pelvis to the right in the backswing a slight bit (1-2 inches) is common, as players will shift pressure into their trail foot at the same time as they load the club going back. The key with sway is to understand that if the body sways in the backswing it will need to re-center in the transition/downswing. Players who get into trouble with sway either sway too much in the backswing (more than a few inches), or don’t re-center themselves soon enough in the downswing. At impact you want the pelvis (especially) more forward (toward the target) than it was at address, so keep this in mind as you work on the lateral movement of your golf swing.