One who dreams about food in the middle of the night, gets out of bed and into the fridge. A person who enjoys a snack or two at midnight, no guilt involved.
That fat ass, ain't he a midnight snacker!
Zombies (or Living Dead) that wake up at midnight, and come out of the ground to attack your house and eat your brains. This particular breed of zombies only eat brains, and only wake up at midnight. They're attack ends before the sun comes up.
GJ: It's midnight.
Mikey: The midnight snackers are coming.
Kyle: Protect my brains!
Stripper: I don't have any brains!