Chefs use cooking terms to quickly and easily communicate exact directions.  For example, a recipe for home cooks might say "3 tomatoes, peeled, seeded, and diced into 1/4- inch pieces."  A professional recipe could say "3 tomatoes, concasse - small dice."  In the fast pace of a commercial kitchen, speaking this special language means both efficiency and clear understanding.

Knife Cuts

A critical skill for any chef is cutting.  Each size of cut has a name.  You can find the names, dimensions and even scale drawings of the most common cuts here.

Terms

Blanche
Cooking briefly in boiling water or hot fat and then chilling.  Usually used to par cook an item which will be fully cooked at a later point. Also used to stop ripening in fruits or vegetables before freezing them as well as to make peeling easier or to remove undesirable flavors or brighten color.

Boil
Cooking in water or other liquid that is bubbling rapidly at 212 degrees F at sea level and normal pressure.

Braise
For meats - cooking in small amount of a liquid, usually after preliminary browning and with a cover.   For example a pot roast is browned and then water is added to come about three fourths up the side of the roast.
For vegetables - cooking covered in a liquid, usually without preliminary browning but with a cover.

Deep-fry
Cooking submerged in hot fat.

Fry
Cooking in hot fat.

Poach
Cook gently in liquid that is hot but not boiling - about 160 - 180 degrees F.

Roast
Cook food with hot, dry air in an oven or on a spit over an open fire.

Sauté
Cooking quickly in a small amount of fat.

Simmer
cooking in liquid that is bubbling gently, about 185 - 200 degrees F.

Sweat
Cooking in a small amount of oil over low to moderate heat.  Usually used to reduce the amount of liquid in onions and celery.  Cook until translucent but not beginning to color.