An order is a directive you give to an ally in the heat of battle. When you use an ability with the order trait, you issue a command that grants a specified effect or allows a particular action to a willing ally who can see and hear you, as if the effect had the auditory and visual traits. The ally may choose whether or not to follow the order.
Usually an order effect requires the ally's reaction, though some can be performed as a free action, as detailed in the effect's description.