folklore (and all other uses of 'folk' as a prefix) is not a scientifically fixed concept, it is an umbrella word that can be described but not easily set down...
.,,.

...and also surprisingly modern; first used in English [presumably derived from German volks], it appears, by W J Thoms in 1846 (see my entry on 'Folklore' in The Continuum Encyclopedia of British Literature - 2003). Before that such terms as "popular" [as still used later on by Child], "household" [as in the translations of the Grimms' collections of German folktales] &c would be used.

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