Mitch, I don't know anything about "lappleather" but they mention half tanned quite a bit over on the British Blades forum. Once again I have zero actual experience but I am given to understand it is just what the name implies, a partially tanned leather. It seems to be available only in the European markets. I think Martin Swinkels who used to frequent here uses it quite a bit, as do many of the makers over there.
Chuck Burrows may have a little better information than I do.
Paul