the.com/nursery rhyme

means A short, simple rhyme or song passed down for children, usually easy to memorize and often centuries old.

from The word 'nursery' (the children's room) is medieval, but 'nursery rhyme' as a phrase is surprisingly recent — it only caught on in the 1800s. Before that, these verses were just called songs or ditties, traded by word of mouth for generations with no fixed name at all. Many of the rhymes themselves are far older than the label, drifting up from folk song, street ballad, and political satire — which is exactly how something as cheerful-sounding as 'Ring a Ring o' Roses' could carry such dark rumored baggage, even if historians now doubt the plague connection is literally true.