http://en.wikipedia.org/wiki/Hollow_grind
Thats something I found when I was unsure of what they meant by a hollow grind. an axe grind and a concvex grind are the same thing, in case you didnt realize. Also, mike is indeed a neat guy. It was nice to meet him a few weeks back. sometime I hope to go visit his shop, if I get the chance. Say hi for me, if you would.