The Danger Zone is more commonly known as the "aggro bubble", the white translucent circle around your character on the radar. It determines when NPCs become aware of, and subsequently hostile to, their foes. Exceptions to subsequent hostility include most creatures with level 1-2 in starting areas, like Juvenile Bladed Termites in Normal mode.
In skill descriptions, earshot range is the approximate equivalent of the Danger Zone. Unless otherwise stated, skills which target specific foes can be activated on targets anywhere inside the Danger Zone; if a target is outside the Danger Zone and you have not suppressed actions by holding down Shift, your character will automatically move towards the target until you are within maximum range of the spell activating. It should be noted that this movement is not always the optimal way of getting within range, but the most conventional. (E.g. if your target is on a bridge, and you are below it but outside the Danger Zone, your character will start finding a way of climbing the bridge until they are within range, even though it would be possible to be within range by simply walking under the bridge, as aggro is not affected by the Z-axis. Heroes and henchmen do the same as what your character automatically does when their target is out-of-range.)
- Some creatures, like the Kournan Spotters, have an increased aggro range and will cause their mob to move and attack you from farther away.
- Some creatures have the default ranged attacks longer than radius of visible Danger Zone (like some Kappas in Hard mode). After they have noticed you, they will attack and follow you, being outside of the "aggro bubble".