It is a term from logic. In Latin, it’s “petitio principii.”
It means appealing to a proposition as proof of its own truth.
Discussions of abortion are a gold mine of logical fallacies, especially begging the question: You know: “An unborn baby is not human because it’s not human until it’s born.”
Someone, sometime, got the notion that “begs the question” means “suggests the following question.”
These days, I’m surprised to hear the phrase “begs the question” used correctly. I’m afraid it’s too late, though; enough dimwits think it sounds all intellectual while having no idea what it really means.