What is? presumes a singularity. The problem is in the question. As Karl Popper wrote 'What is' type questions are typically unhelpful.

That's not strictly true, and certainly true not in this instance where we're not dealing in a singularity of concept, even if we treat the noun as such. Rather like Pilate asking What is truth?, I'm sure he wasn't presuming a singularity, however so rhetorical his inquiry. No such rhetoric here of course, and pragmatically it works a treat, so the only thing unhelpful thus far on this thread is your pointless post which I nevertheless feel compelled to respond to. So thanks for that, Tug.

The entire body of ancient popular beliefs, customs, and traditions, which have survived among the less educated elements of civilized societies until todav.

Does Folklore have to be ancient? And can we still talk about less educated elements of civilized societies as being passive carriers of a lore the true significance of which they, as lore-carriers, can't possibly understand? I have no problem with this, by the way, just as I don't expect the grief-stricken mother who carefully curates the road-side shrine to her child who was killed by a passing car some years earlier to be able to tell me about the full folk-history of wayside shrines, much less why she is compelled to externalise her grief in such a way.