Sculpture in which figures or other images are attached to a flat background, they are raised from the plane of the composition. Often this work is described as bas-relief or haut-relief. Source: "The World&#39;s Greatest Paintings", The Teaching Company<br><br>The apparent or actual (impasto, collage) projection of three-dimensional forms.<br><br>In sculpture, any work that projects from the background. Reliefs are classified by degree of projection. Relief sculpture is distinguished from sculpture in the round. In a bas relief (low relief or basso-relievo in Italian), the figures project only slightly and no part is entirely detached from the background (as in medals, coins, or areas of large reliefs in which the chief effect is produced by the play of light and shadow). In a haut relief sculpture (high relief or alto-rilievo), the figures project at least half of their natural circumference from the background. Between these two is the demi relief (half-relief or mezzo-relievo). The lowest degree of relief in which the projection barely exceeds the thickness of a sheet of paper is called a crushed relief (relievo sticciato or schiacciato). There is also a relief in reverse, called hollow relief, in which all the carving lies within a hollowed-out area below the surface plane, and which, through an illusion of depth and roundness, looks like raised relief. Hollow relief, also called sunk or concave relief (cavo-relievo), incised relief (intaglio-rilievato) are the kind of carving done on gems by the Greeks and Romans. Reliefs may be carved from hard materials or modelled in wet clay, softened wax, or plaster. Reliefs are often elements of architectural sculpture.