Patrol

From Guild Wars Wiki

The term patrol refers an NPC or party of NPCs, usually hostile, which moves along a set path rather than wandering around within a small radius or standing still.

Learning to aggro and separate a patrol from other groups is a key tactic in making encounters with numerous hostiles easier and vital in surviving difficult areas of the game.

The allegiance of patrols may differ from one patrol to another on the same map, so sometimes patrols will fight each other without player intervention.