Bore - The diameter of a cylinder
Stroke - The distance the piston moves
Head Gasket Thickness - Self Explanatory
Deck Height - The distance between the flat surface (not the dome or dimple) of a piston, and the top of the cylinder, while at TDC (Top Dead Center). This should be a negative number if the piston goes beyond the top of the cylinder.
Piston Top Volume - The volume of the dimple, or dome in the top of the piston. This should be a negative number if the piston has a dome, and a positive number if the piston has a dimple. This is because a dome will take away volume from the combustion chamber, and a dish will add more volume
Combustion Chamber - The volume of the combustion chamber