Exactly what is gesture drawing?

Why is it called a "gesture" drawing.
One tutorial decribed it as being to do with the hand movements you make, gestural movements.
http://www.mmwindowtoart.com/gesturedrawing.html
But I don't like the results on their, so I'm reluctant to follow it

Some talk about looking once, and then drawing what you remeber, some talk about flashing the eyes back and forth.

Why is it that there so helpful for improving in drawing? Just how helpful and for what?

Is it better to keep the hand moving, or be selective in the lines you choose?

How quick is it? Is it good to time the drawings?

Details, too little and it looks crap, too much and it looks crap and takes loads of time. hmmm.

What everyone seems to agree on, is that it is about capturing the "essence". This is a very annoying way to describe it, although I think I started to grasp it

Is it more focused on flat 2d shapes, or 3D?

When I see trees and their movements, I like to think of them as a sound. Shooting up trunks go SCHUUM, or twirly leave going fltrfltrfltr, and this seems to get the most satisfying results for me.

Any thoughts?