What brands are “designer”?

Is it clear to anyone how brands are selected as “designer”? Some are obvious but seeing Kate Spade, Vince, Alice & Olivia, Rag & Bone etc etc doesn’t make a tone of sense to me. Theres tons of other brands of similar price point, quality and “status” that aren’t included in the designer category. Does it seem very arbitrary or do I just not understand fashion (fully possible).