The term "4th Gear," in relation to surfing, was coined by Greenough when describing a level of speed that transcended riding in the curl of the wave.
In George's world-view, first gear is riding along the wall at the speed of the curl. In essence, it's riding as slow as you can go and still make the wave.
Second gear is when you have enough speed to turn up and down, or back and forth, on that same wave, covering the same total distance as you would in first gear...but at a higher rate of speed over the water because you're moving up and down rather than in a straight line.
(Paul Masiel and I in first gear at the right. Greenough in second at the left.)
Third gear is when you have enough speed to break loose from the wave and travel out and over distant sections.
The size and quality of the wave isn't an issue, either. You can hit third gear in foot high slop!
Fourth gear is when you're going so fast that you're surfing completely beyond the speed of the curl...often riding up in the lip of the wave as it fringes in front of you.
When the Standard became tuned in (back in '84/85) George commented that it was the only mat that he'd ever surfed that he could to hit 4th gear on. Not long after, it became the name of our mats!