The primary grind is where a knife

Knife

A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...

 first begins to narrow into a cutting edge from the thickness of the main stock of the blade

Blade

A blade is that portion of a tool, weapon, or machine with a cutting edge and/or a pointed tip that is designed to cut and/or puncture, stab, slash, chop, slice, thrust, or scrape animate or inanimate surfaces or materials...

. The cross-sectional shape of the blade of a knife or sword

Sword

A sword is a bladed weapon used primarily for cutting or thrusting. The precise definition of the term varies with the historical epoch or the geographical region under consideration...

 is made up of different planes, or grinds. The sharp, cutting edge of the blade is often further ground at a secondary, or 'edge', bevel. This allows the blade to have more functions than otherwise possible with a strictly wedge or chisel shape.

The Swiss Army Knife

Swiss Army knife

The Swiss Army knife is a brand of pocket knife or multi-tool manufactured by Victorinox AG and Wenger SA. The term "Swiss Army knife" was coined by US soldiers after World War II due to the difficulty they had in pronouncing the German name....

is an example of a knife with a primary bevel and an edge bevel. By contrast, a blade composed of a single flat grind from stock thickness to the cutting edge is known as a 'full flat ground' blade. The cutting properties of a blade are determined by the type of metal, the hardness of the blade, and the grinding pattern (e.g. convex, concave, teardrop).