Relief Painting is a sculptural technique, where the sculpted elements remain attached to a solid background of the same material. Generally done using clay, mud or plaster of paris.
To create a sculpture in relief is to give the impression that the sculpted material has been raised above the background plane.
They are further subdivided into three types based on the amount of relief - low relief, medium relief and high relief. Low and medium relief generally being more two dimensional and high relief being three dimensional.