It is a French tradition, which occurs just before the dinner.
It is when you drink couple of drinks (especially alcoholic stuffs) and you eat some chips, peanuts, almonds, ...
The goal is to prepare your stomach to eat, and to have fun of course!!
Emmanuel : Hey Eric do you want to come over for dinner?
Eric : Of course dude! Do you want me to bring something for the predinning?
The act of walking around a night club or other social setting and scanning the room for the opposite sex to approach and begin seducing. This behavior is very obvious to others and the body language of the subject looks like that of a wild predator looking around for a viable prey.
That horny old man who is staring at those pre-teens ain't fooling anyone - he's preding.