It is something that a very cool and nonchalant person has. The more embarrassing things you do, the less aura you have. The more cool things you do, the more aura you have.
Person 1: did you see those two people do the perfect dap?
Person 2: yeah! That was so cool, I can feel their aura!
Aura is a brainrot term, which refers to the coolness or reputation gained from doing an act. Having a high amount of aura means that you possess a high reputation. "Negative aura" means that you're uncool, and have a bad reputation.
Person 1: I just slipped on dog poop lol.
Person 2: -69420 aura.
Person 1: You are a disappointment to your family.