A herb (pronounced "urb" in American English and "hurb" in most varieties of Commonwealth English) is a plant grown for culinary or medicinal value. The green, leafy part of the plant is typically used. General usage differs between culinary herbs and medicinal herbs. A medicinal herb may be a shrub or other woody plant, whereas a culinary herb is a non-woody plant. By contrast, spices are the seeds, berries, bark, root, or other parts of the plant, even leaves in some cases. Culinary herbs are distinguished from vegetables in that they are used in small amounts and provide flavor rather than substance to food.

Oregano is a conditio sine qua non in Italian cuisine, where it is used for tomato sauces, fried vegetables and grilled meat. Together with basil, it makes up for the character of Italian dishes; see parsley on Italian variants of bouquet garni.

Oregano can effectively combined with pickled olives and capers or lovage leaves; other than most Italian herbs, oregano harmonizes even with hot and spicy food, as is popular in Southern Italy. The cuisines of other Mediterranean countries make less use of it, but it is of some importance for Spanish, French and Greek cooking.

The dish most associated with oregano is pizza, a kind of open pie: Bread dough topped with tasty stuff and baked. Bread of this kind was probably eaten in Southern Italy for centuries; according to the legend, pizza came into existence in 1889, when King Umberto and his wife Margherita sojourned in Napoli (Naples). Pizza, at this time not more than white bread flavoured with tomato paste, was then a popular food for the poor masses. To honour the Queen, a local baker devised a richer kind of pizza: In addition to the red tomato paste, white mozzarella cheese and green basil leaves were employed, thus reflecting the colours of the Italian flag. This invention became known as pizza Margherita and spread all over Italy and, with some delay, over the rest of the world.

Today's pizza relies more on oregano than on basil, and use a multitude of further ingredients: Ham, sausage, fish, shellfish, mushrooms, artichokes, onion, garlic, olives, capers, anchovies and more make pizza a sophisticated delicacy, although it had once been the poor man's sandwich.

Basil is most commonly used fresh, and in cooked recipes, is generally added at the last moment, as cooking destroys the flavour quickly. The fresh herb can be kept for a short time in plastic bags in the refrigerator, or for a longer period in the freezer, after being blanched quickly in boiling water. Place fresh leaves in a dry jar with a pinch of salt, and cover with olive oil. The dried herb also loses most of its flavour, and what little flavour remains tastes very different, with a weak coumarin flavour, like hay.