On Wikipedia, notability is a test used by editors to decide whether a given topic warrants its own article. For people, the person who is the topic of a biographical article should be “worthy of notice” or “note” — that is, “remarkable” or “significant, interesting, or unusual enough to deserve attention or to be recorded” within Wikipedia as a written account of that person’s life. “Notable” in the sense of being famous or popular — although not irrelevant — is secondary.
This notability guideline for biographies reflects consensus reached through discussions and reinforced by established practice, and informs decisions on whether an article about a person should be written, merged, deleted, or further developed.
Each day of the year has its own page, with a list of births and deaths on that date and a link to the article on each person; we may safely assume that anyone listed thereupon is “notable.” This was the bottom of the “Births” section for the May 6 page:
Yep. His Royal Smallness, age somewhere around one day, is notable by dint of royal birth. Our congratulations to the Duke and the Duchess.