to clay a car

I'm new to this soprt. what does it mean to CLAY a car?
..........PIP

The term claying a vehicle is referring to lightly glide a clay bar which is the size of a soap bar over the painted surface. This bar looks like a bar of silly putty & you can use it with a lubricant or water & soap solution & the bar will remove any industrial fallout along with jet fuel or any light debris.

This claying method is not to be confused as a paint cleaner. It is intended to be used to only remove any light contaminant that has fallen on the exterior painted surface.