Aggro

Aggro is a slang term meaning "to cause hostile NPC mobs to attack by getting too close to them." The mini-map located in the upper right hand corner of the screen displays a white transparent circle that surrounds your character. Any mob (indicated by red dots) that even slightly enters this circle (often called your "aggro bubble") immediately becomes aware of your presence and is aggravated, causing it to attack you. Careful understanding and awareness of your bubble is very important, especially if your teammates are low on health/energy or already attacking another group of enemies.