Diving in soccer is the practice of immediately falling to the ground when a foul has been committed against you (or even if one hasn't) in order to get the referee's attention...much of the time there's only one referee and two assistants for that huge field and you're gonna get held and tackled badly so how else are you going to get that call? You dive.
Except for Lionel Messi. It's not that he never dives (he does) but he stays on his feet more often than not while facing perhaps....