The hook
Also said as Elevator pitch, USP, Unique selling point
The one thing that makes someone who has never heard of your game want it, said in a sentence. It needs to be something they can imagine doing and have not seen before.
If you cannot say it, nobody can repeat it to a friend. A long list of features is what you write when you do not have one. Find out early, since a weak hook is far cheaper to fix before you build the game than after.
Say it
“Before we build more levels, write the hook on a card. Show it to ten strangers, and if they can't tell you back what you do in the game, we fix the card or the game.”
Where you’ve seen it
Balatro calls itself a poker roguelike. Papers, Please: you are a border guard stamping passports in a police state. Both explain themselves in one line and leave you curious.
Not to be confused with genre
A genre says what shelf you go on. A hook says why you are the one to take down. "Roguelike deckbuilder" is a shelf. "A poker roguelike" begins to be a hook.