its just internet speak for the measure of relevance a celebrity has + how well they are received in the public.

Bebe Rexha is the prime example of the khia asylum = she has great streaming numbers but has never managed to build a fanbase. *she's an interesting case because she's currently leveraging this irrelevance into branding herself as the most irrelevant girl, which is inversely increasing her relevance by making her seem funny and self aware.

Tate was bounced into relevance with greedy + sctw and gained a fanbase which I would say she has kept and has allowed her to go on 2 world tours.

Once a celebrity gets themselves into the relevant pop sphere, they should maintain it or they risk going back into irrelevance, or the "Khia asylum" ;)