It means of or pertaining to Nice, France. Dishes that are served à la niçoise are characterized by ingredients common to the south of France - black olives and olive oil, tomatoes, garlic, green beans, potatoes, and anchovies.

The niçoise dish best known in this part of the world is Salad Niçoise, but there are many classic dishes and variations. A niçoise fish garnish consists of tomatoes, sautéed garlic, capers, lemon juice, anchovy butter, and black olives. A niçoise garnish for meat consists of diced fried tomatoes, garlic, green beans, and potatoes. The classic niçoise sauce is made with mayonnaise, pimientos, tomato puree, and tarragon. Soups à la niçoise are usually garnished with cubed tomatoes, chervil, and green beans.

Poulet à la niçoise is chicken sautéed in oil and seasoned with saffron, garlic, tomatoes, and a bouquet garni, which is cooked in a covered dish in the oven. The pan juices are then mixed with white wine, garlic, and tomato puree. The chicken is traditionally served with zucchini sautéed in butter, new potatoes, and black olives.

Kind of makes you want to plan a trip to the south of France, doesn't it?