What are facebook app "push notifications"?

[Jordan]

On my iphone 4 I have two Facebook settings, one is under "notifications" the other one is under "Facebook". I don't know what "push notifications" are, and if they have anything to do with the "notification facebook setting". When I turn push notifications off I still receive notifications from facebook almost instantly even when I have another app open.

[Zulu]

They push information to your phone, and it shows up like a text message would.

For instance, if someone were to write on your wall, if you had push notifications turn on, you'd get a notification on your phone saying "So and so has written on your wall"

Simple as that!