Aggro

Aggro, short for aggression, is an invisible statistic that determines the distance at which enemies will begin to attack the player.

All enemies target the player based on criteria set in their AI. Most will constantly try for a target, while others may only target if the player is in water, for example.

Armor and other items that "increase/decrease enemy targeting" cause enemies to consider a player to be closer or farther away than they actually are. Certain accessories, armor, and other sources in the Calamity Mod affect Aggro.