Dynamic paint is a modifier and physics system introduced in Blender 2.6x that can turn objects into paint canvases and brushes, creating vertex colors, vertex weights, image sequences, waves, or displacement. Use this tag for all of your questions pertaining to the use of Dynamic Paint.

Dynamic paint is a modifier and physics system that can turn objects into paint canvases and brushes, creating vertex colors, image sequences or displacement. This makes many effects possible like, for example footsteps in the snow, raindrops that make the ground wet, paint that sticks to walls, or objects that gradually freeze.Dynamic Paint can be activated from the “Physics” tab of the “Properties” editor.

Dynamic Paint at the Blender Manual