A “hook” is any feature that makes a song memorable. It could be a distinctive rhythm, a sound, a melody, a lyric, anything that catches the ear of the listener and sets a song apart from others.
People like to hear hooks repeat themselves; they are why we buy certain music and listen to it over and over; the music industry is obsessed with them.
Lyrics can be hooks, like the “yeah, yeah, yeah’s” in The Beatles’ “She Loves You,” or The Clash singing, “Should I stay or should I go now?” There are rhythmic hooks, like the distinctive Bo Diddley beat used in Buddy Holly’s “Not Fade Away,” or the strangely satisfying bass drum interruptions in the song “Tainted Love.” Pretty much every hip-hop sample is a hook.
Some hooks come in the form of guitar riffs: “Satisfaction,” “Smoke on the Water,” and every song by AC/DC. More unusual instruments work well, too, like the weird theremin sound in “Good Vibrations.”
Lots of times these come off as gimmicks, and can turn a song into an annoying earworm. But if you try to avoid hooks, know that your brain chemistry will work against you. Anticipating and then hearing a hook stimulates a little squirt of dopamine, the neurotransmitter associated with rewarding behavior and pleasure. This is true even if you don’t like the song.