Airlines are companies that provide air transportation services for passengers and cargo. They operate aircraft to carry people and goods from one location to another, often over long distances. Airlines can be classified into different categories, such as commercial airlines, which serve the general public, and cargo airlines, which focus on transporting goods. Most airlines offer various classes of service, including economy, business, and first class, each with different levels of comfort and amenities. Major airlines often have extensive networks, connecting numerous cities worldwide, while smaller regional airlines may serve specific areas. Popular examples of airlines include American Airlines, Delta Air Lines, and Emirates.