In this context aura is a dynamic variable of how cool you are as a person. It is universally agreed that everyone starts at exactly 0 (“nobody is born cool”).

Aura as a concept is very social so each persons aura and the factors determining it depend on current social setting.

Aura farming is any voluntary (often repetetive) act to increase and prove your aura in the eyes of an observer.

All of this is mostly ironic or banter, a joke based on the concept of a global and definitive leaderboard or ranking.

Its basically like flexing your net worth “in the realworld” but instead of it being a monetary thing its a deeper judgement of character.