O'Brien Potatoes - A dish of diced potatoes, onions, and sweet peppers or pimientos, fried until browned and crisp.

Oeuf - The French word for "egg."
Recipe: Eggs Sardou
Deviled Eggs à la dijonnaise

Okra - A vegetable brought to the U.S. South by African slaves. Okra pods are green and ridged. When cooked, okra gives off a viscous substance which may serve as a thickener in some dishes.
See: Okra Information & Recipes

On the Half Shell - This phrase usually describes oysters served on the bottom shell, either raw on a bed of crushed ice or cooked on a bed of rock salt.
Recipe: Oysters Casino

Orange Roughy - A mild flavored New Zealand fish with white flesh, orange roughy is also low in fat.
Recipe: Oven Fried Orange Roughy

Oregano - A pungent herb, similar to marjoram. Oregano can usually be found dried, ground, or fresh.
Recipe: Romano Oregano Bread

Orgeat Syrup - A sweet syrup used in cocktails, orgeat syrup is made with almonds, sugar, and rose water or orange-flower water.

Oxalic Acid - Oxalic acid is found naturally in many plants, but is poisonous in excessive amounts. Spinach, rhubarb, sorrel all contain measurable amounts of oxalic acid. It actually forms insoluble compounds with calcium and iron which inhibit their absorption by the human body, thus diminishing the purported nutritional value of some vegetables, particularly spinach.

Oyster Mushroom - A smooth-capped mushroom with a fan shape and mild oyster-like flavor. They're found dried or fresh in many supermarkets and most oriental markets.