Each piece of equipment is part of a set.
Specific pieces of Helm, Chest, Boots, Shield and Broadsword might consist of a 5-piece set of equipment.
Specific pieces of Amulet, Ring and Pendant might consist of a 3-piece set of equipment.
The more pieces of a set you have, the greater stat bonus your character can obtain. T
he Set Stats are displayed on the bottom of the page for equipment stats.