Grind is defined as the transectional geometry of a blade. Blades can be straight grind with a wedge shape, hollow grind with biconcave sides, or transitional grinds. Full hollow grind blades have a belly or ridge which gives the thin metal torsional resistance.
The terms 1/1 and 1/4 hollow grind indicate the degree of hollow grind, but also point to the parts of a full hollow grind blade below and above the belly. The former definition distinguishes different types of razor blades, the latter refers to the successive phases in the production process.
When the blade rests on a flat surface, the sides of a straight grind blade touch the surface. However, only the back and the edge of a hollow grind blade touch the surface. The belly never reaches the surface. These differences between straight- and hollow grind blades are essential for the process of sharpening.