What is a direct vent furnace?

We need a chimney liner for our gas furnace and a contractor told my husband to look into a direct vent furnace because they are energy efficient and about the same price as the chimney liner. On google, the only results I am getting for direct vent furnaces are these little space heater looking things that you install in rooms. Can he be mistaking the direct vent furnace for some other type of furnace? (We have gas heat and radiators.)