Subway is a fast food chain specializing in "submarine" sandwiches and salads. Subway was founded in Connecticut in 1965, and today it is the third largest restaurant operator in the world. They also introduced healthier breakfast foods and lower-fat pizzas.
Subway's ad campaigns have focused on the health benefits of their food compared to other fast food, and this is one reason they have grown so much.
Like most fast food chains, Subway is a franchise chain. However, most chains directly own some locations, whereas Subway does not.