Instead of a generic URL, a company or a person uses an individually suitable, ideally personally chosen URL within a website.
Vanity URLs are typically required within the social networks.
www.facebook.com/crispycontent is an example for a vanity URL, www.facebook.com/c243mk65 is a generic one.
The vanity URL has a stronger visual impact and a stronger relevance for SERP. The URLs of social media profiles can thus shared more easily and they can be advertised in the classical media.