Alan Freed was a DJ, but is more famous for being the guy who successfully campaigned to give the name Rock & Roll to the genre of boogie-woogie that had been developing for the previous twenty-plus years.
Boogie-woogie, itself a fusion of gospel, blues, and honkie-tonk, had been using the terms “rocking” and “rolling” to refer to both music and sex, since at least the 1920s. This term had come from gospel/religious music, where it described excitement in the name of Jesus, and had arrived in THAT genre from naval terminology, because a ship’s deck, and people used to walking on it, rocked and rolled.