The "Hook" is what always sells you the song and makes it live in your memory. Regarding "The Hook" here's the definitive explanation and example from Blues Traveler, 1994.
It doesn't matter what I say
So long as I sing with inflection
That makes you feel I'll convey
Some inner truth or vast reflection
But I've said nothing so far
And I can keep it up for as long as it takes
And it don't matter who you are
If I'm doing my job then it's your resolve that breaks
Because the Hook brings you back
I ain't tellin' you no lie
The Hook brings you back
On that you can rely
The 2016 Hook Is Many Hooks:
And yet fewer and fewer are being hooked....