When adjusting spring preload on a motorcycle, a "turn" typically refers to a 360-degree rotation of the adjusting collar or ring. In other words, one complete revolution around the collar or ring corresponds to one turn. This allows you to increase or decrease the tension on the spring to suit your preferences or riding conditions. It's important to consult your motorcycle's owner manual or refer to manufacturer-specific instructions for precise details on adjusting the spring preload, as different motorcycles may have variations in their suspension systems.