Bas relief is a method of sculpting which entails carving or etching away the surface of a flat piece of stone or metal. This resulting image is raised above the background flat surface. For example, if a stone slab is two inches thick before sculpting begins, then the non-image (background) area might be, say, one inch thick when the art work is done, and the image area will vary between one inch to two inches, depending on the final image.
Bas relief is an art technique that has been used since ancient times, and is still in use today. There are countless examples both on display in museums and in the regular world. Most cultures of the world have utilized the technique. It is most commonly used for the architectural adornment of building surfaces, both inside and outside, where the stone is part of the building, rather than as a free-standing piece of art to be hung on a wall.
Sometimes the resulting image has been painted, and other times it has been left in the natural state of the material used.
Bas relief should not be confused with an etching, as the latter requires cutting into a flat surface, leaving indentations within the flat surface, which becomes suitable for printing by applying ink and pressing paper to the surface.