So, in the future, when you’re wondering “where a word comes from,” there’s a good word to know: Etymology. Etymology is the study of words histories.

From the Wikipedia article on “Rapping”, there is a section on etymology and usage:

The English verb rap has various meanings; these include “to strike, especially with a quick, smart, or light blow”,[17] as well “to utter sharply or vigorously: to rap out a command”.[17] The Shorter Oxford English Dictionary gives a date of 1541 for the first recorded use of the word with the meaning “to utter (esp. an oath) sharply, vigorously, or suddenly”.[18] Wentworth and Flexner’s Dictionary of American Slang gives the meaning “to speak to, recognize, or acknowledge acquaintance with someone”, dated 1932,[19] and a later meaning of “to converse, esp. in an open and frank manner”.[20] It is these meanings from which the musical form of rapping derives, and this definition may be from a shortening of repartee.[21] A rapper refers to a performer who “raps”. By the late 1960s, when Hubert G. Brown changed his name to H. Rap Brown, rap was a slang term referring to an oration or speech, such as was common among the “hip” crowd in the protest movements, but it did not come to be associated with a musical style for another decade.[22]

Rap was used to describe talking on records as early as 1970 on Isaac Hayes’ album …To Be Continued with the track name “Monologue: Ike’s Rap I”.[23] Hayes’ “husky-voiced sexy spoken ‘raps’ became key components in his signature sound”.[24] Del the Funky Homosapien similarly states that rap was used to refer to talking in a stylistic manner in the early 1970s: “I was born in '72 … back then what rapping meant, basically, was you trying to convey something—you’re trying to convince somebody. That’s what rapping is, it’s in the way you talk.”[25]

Sometimes said to be an acronym for ‘rhythm and poetry’, this is not the origin of the word.[26]