Shield set

From Guild Wars Wiki

A shield set, also known as a defensive set, consists of a one handed martial weapon and a shield for which the req may or may not be met. It is generally regarded that every single character should carry one of these sets (usually one for every kind of armor bonus damage type and possibly others such as cripple reduction) in PvP situations to reduce the damage received when under fire. Specific mods chosen can vary slightly, but the goal is to increase the survivability of a character at the cost of other beneficial weapon mods such as enchanting mods or skill recharge mods.

Any disadvantages that arise from being inside a shield set can easily be removed by simply swapping back to another set before casting a spell or attacking a target.

While considered necessary in PvP, shield sets can also be useful in PvE.