Kettle Corn (Method) is one of the basic types of Popcorn preparation. It is popcorn and oil in a heated kettle/pot that is constantly heated and stirred. As the Corn pops, it absorbs some of the oil. The denser seeds stay to the bottom and continue to heat until most of them pop. The popcorn mostly stays in the the Kettle during this process unless is spills out. Most kettles are electrical heated.
While Most of the fresh popcorn you buy is Kettle corn, Modern Machines are refereed to as old / old school, in light of newer at home methods like Air Popped, and Microwave Popcorn.