Each enemy in Aura has some kind of element, the basic four being Air, Earth, Fire and Water.
Then there is Chaos, Neutral and Poison.
The basic elements have only one weakness (not including Chaos) whilst being resistant to the prior element, for example - Air is weak to Earth but Resilient to Air itself.
Chaos has shown to have a universal damage multiplier to the main four elements while only doing reduced damage to neutral aligned enemies.
Neutral attacks can be simply put as physical attack as in, a normal weapon with no element.
Poison is somewhat similar to neutral with only the reduced damage against the same element.
Tables of Elements
Note: - The "Offensive" side is the element done by the attack on the target. - The "Defensive" side is the element of the target.