Rock 'n Roll The 1950s
Disc jockey Alan Freed is universally credited with applying an expression that had existed for decades to a music that had existed for years (known as rhythm and blues, sepia music, or race music) to give the young of the world rock and roll. Freed used the phrase as the theme of his popular radio show in Cleveland, "The Beat Beat," which he changed to "The Moon Dog House Rock-'n'-Roll Party." As Wes Smith wrote in The Pied Pipers of Rock 'n' Roll "while he may not have been the first to play the music, he was the first to put it all together in one package and peddle it to a big audience of both blacks and whites." The phrase rock and roll was used prolifically in song lyrics for three decades before Alan Freed's inspirational appropriation of it, almost always as a euphemism from the black vernacular for sex. Examples include:

1922
Trixie Smith and the Jazz Masters:
"My Man Rocks Me (With One Steady Roll)"

1932
Boswell Sisters: "Rock and Roll"

1934
From Transatlantic Merry-Go-Round, a Jack Benny movie:
"Rock and Roll"

1938
Bunny Berigan and His Orchestra:
"Rocking Rollers Jubilee"

1938
Hot Lips Page:
"Rock it for Me" ("Rock and roll...")

1939
Buddy Jones: "Rockin', Rollin' Mama"

1950
John Lee Hooker: "We're Gonna Rock, We're Gonna Roll"

1951
Clyde McPhatter and the Dominoes:
"Sixty Minute Man" ("Rock and roll all night long...")

1952
Nugetre:
"Ting-A-Ling" ("All these girls 'bout to drive me wild/The way they rock and roll and call me angel child")

1947
Wild Bill Moore: "Rock and Roll"

1951
Treniers: "It Rocks! It Rolls! It Swings!"

1952
Lil' Son Jackson: "Rockin' and Rollin'"

1952
M. Jackson:
"Rockin' and Rollin' No. 2"

1952
Wards-Marks:
"Pedal Pushin' Poppa" ("I'll rock your soul and make you roll - a pedal pushin' poppa I am")

From the start, rock and roll was often referred to in the clipped form of simply rock, which itself boasted two slang meanings. Like the full expression, rock standing alone was a euphemism for sex. Trixie Smith's "My Man Rocks Me (With One Steady Roll)" left no doubt as to its meaning in 1922, and neither did Laurie Tate and Joe Morris's "Rock Me Daddy" in 1952-"They rock in the park, down in lover's lane/Like it in the mornin' when it's pourin' down rain." In the same year, P. Harris wrote "Rock, Rock, Rock" with its explicit reference to sex-"We rock on the sofa, we rock on the chair, we rock on the table and we don't care." Secondly, the term rock had been used for years in connection with a band or song that conveys energy and passion, as illustrated by the February 12, 1947, Steve Canyon comic strip, which features our hero in a night club, telling his date Miss Calhoon that "That band rocks easy!"