The Carrefour stores in the game are Landmarks that function as Retail shops of the three respective densities. They are based off real shops in France ran by the company Carrefour. We have:

Carrefour City (light density shop)

Carrefour Market (middle density shop)

Carrefour Hypermarket (high density market)

All of them earn very nice taxes, but in addition to their food consumption, they require access to Passenger services.