A hook, used in load of songs, is an aspect of popular or commercial music that "grabs" people and makes it easy to like like or remember the song. For example, the riff from "Son of a Preacher Man" used in Cypress Hill's "Hits from the Bong"  is an example of a hook. "Check out the hook while I drop crazy rhymes" -- ??? (???).
"Check out the hook while my DJ revolves it..." - Vanilla Ice (Ice Ice Baby)
Also, the word hook in Detroit(where I'm from)means the police
A Gangsters Disciple's name for a Vice Lord, meaning (Hoover Over Other Kingdoms).