Upon liking or commenting a photo/status/wall post on Facebook, you have tons of notifications from other people who have commented on that photo/status/wall post.
Friend 1: Man... I got tagged in one of those "Type of Friend" photos today.
Friend 2: What's so bad about that?
Friend 1: I logged out, then back in an hour later, and I had 65 notifications saying that someone else kept commenting on that photo.
Friend 2: Bro, I'm sorry. You got totally notification bombed right there.
The act of getting a group of people to all get on to a certain person's Facebook page and like everything on that page. When that person gets on Facebook later, they will have hundreds of notifications.
Ex. John: "Dude I got onto Facebook and had 143 notifications! I was excited until I realized it was because of you asshole dropping a notification bomb on me."