Aura

From Diablo Wiki

Aura is an influence that you can experience if you are near certain Unique Monsters, or if you are a Paladin or near one. Auras can be offensive or defensive. An example of an offensive Aura is the Holy Freeze Aura, which slows the target and inflicts Cold damage. An example of a defensive Aura is the Paladin's Resist Lightning Aura, which increases the Lightning Resistance for the Paladin and all party members.