Orly Airport (ORY; official name, Aéroport de Paris-Orly) was built in 1932 and has always served as a secondary airport, first to Le Bourget and now to Charles de Gaulle. However, with almost 30 million passengers per year, it could hardly be considered a lesser airport. Orly mostly serves low-cost and regional airlines that fly within Europe, with many flights to former and current French colonies in Africa and the Caribbean. One airline goes to North America (Open Skies to New York's JFK).
Travelers should note that because of its regional dominance, Orly serves as a major connecting flight hub. This means that although a long-haul flight may land at Charles de Gaulle, the connecting flight could take off from Orly. Check itineraries carefully before booking, and make sure that there is at least six hours between flights to ensure proper immigration/customs/baggage claim/check-in time.