Picnic: 'a pleasure outing at which a meal is eaten outdoors'.

Picnics and cookouts - plain and fancy - are synonymous with summertime, and Memorial Day marks the start of the season for much of the country. The dictionary defines picnic as ''a pleasure outing at which a meal is eaten outdoors.'' This is especially true for urban people, for whom an outdoor meal is a luxury.

But there's nothing new about picnics, barbecues, or cookouts. Artists have for years portrayed people enjoying a picnic lunch in a forest clearing or at a regatta.

In 17th-century Japan the picnic was especially popular with feudal lords, who ate outdoors from handsome picnic boxes and were entertained by three-stringed instruments called samisens.

In France, lords and ladies enjoyed lavish meals outdoors in huge tents. Czar Alexander III of Russia played host to picnics that included choice caviar and required a full staff, a samovar, a cookstove, and camp stools.

If there's one traditional summer picnic food of our own, it's potato salad. This is about as basic to a picnic menu as you can get. But most people have several favorite foods they associate with outdoor meals.

Hard-cooked eggs, pickles, olives, watermelon, lemonade, and sandwiches come to mind. Some people don't consider a picnic complete without cold chicken. Others want ham, roast beef, and fancy combinations. Still others go in for cold soups and pates and spreads.

You may be one of those spontaneous picnickers who gather a lot of food at the nearest gourmet shop - cold cuts, cold pasta salads, ratatouille, cheeses, fruits, and breads. Sandwiches can be put together on the spot, made with two slices of bread, or with one slice in the Swedish and Danish style.

Ethnic foods and snacks are great for picnics, since many of the same requirements for fast food apply at these informal occasions. They are easy to handle and can be eaten without much equipment.

In the city you can find such food as Japanese sushi and sashimi, Chinese spare ribs, smoked-goose sandwiches, stuffed grape leaves, kabobs, tabouleh, ratatouille, and pita bread sandwiches.

To some people a picnic means grilling food, a method of cooking now popular at many restaurants. Special kinds of wood include mesquite, apple, and lilac wood.

This expands the menu possibilities for picnics, since recipes feature everything from meat, fish, chicken, vegetables, and even salad, cooked on the grill.

Here are some recipes that might add a different flavor to a traditional picnic. The first one is often eaten as a salad or an appetizer. It is a pleasant combination of cracked wheat, with a flavor of mint and parsley. Ingredients can vary in amount according to personal taste. Tabouleh in Pita Bread 1/2 pound cracked wheat 3 tablespoons finely chopped onion Salt and black pepper 1 cup fresh parsley, chopped 3 tablespoons fresh mint chopped 2 1/2 tablespoons red, sweet pepper, chopped 4 tablespoons olive oil 4 tablespoons lemon juice Pita bread

Soak cracked wheat in water for 30 minutes. It will expand. Drain; squeeze out water until quite dry. Add onions, mix well, then add remaining ingredients, except pita bread. Taste for seasoning. It should taste lemony.

Serve in split pita bread rounds as a pocket sandwich.

As a salad, tabouleh is often served with black olives and sweet pepper strips. Also cucumber and tomatoes may be added. Spicy Egg Salad 8 hard-cooked eggs, peeled, chopped 1 small onion, chopped 1 1/2 cups celery, finely chopped 1/4 cup capers, chopped 2 dill pickles, chopped 2 tablespoons fresh dill, chopped 1 2 oz. can anchovy fillets, drained, chopped 1/2 cup mayonnaise Salt and pepper Lettuce Whole wheat bread or crisp rye crackers Crisp, cooked bacon, garnish

Combine all ingredients, adding salt and pepper last. Chill. Spread on whole wheat bread, adding lettuce and a second slice of buttered bread.

For a Swedish-style sandwich, spread on crisp rye crackers and garnish with strips of crisp bacon. Makes 1 quart of sandwich filling.