Ron - There are no stupid questions, and if memory serves this ones been asked before. I think Mark asked me the same thing in an earlier thread.
This is a term borrowed from bridgewrighting, in common usage here in my area, though it seems to be seeing wider acceptance, and was seen in Joseph Conwill’s fine articles on Burr Arch and Paddleford Truss bridges in Timber Framing.
Dap - the simplest of timber joints, literally a plowing though from one face to its opposite, a notch.
