Hovercraft
Hovercraft is a vehicle that floats on a thin layer of air pushed beneath it.
Think of it this way
When you slide a greased pan across a smooth countertop, a thin layer of oil keeps it from touching the surface. The pan glides on that film of oil, not on the counter itself. A hovercraft works the same way. Air pumped under the craft forms a thin cushion that lifts it just off the ground.
Explaining hovercraft by grade level
Blow up a balloon and tape it to a piece of cardboard with a hole. When the air rushes out under the cardboard, it lifts up and slides across the table. The trapped air makes a smooth cushion that stops the cardboard from dragging.