Bas-relief is a type of sculpture that has less depth to the faces and figures than an actual sculpture.  Bas-relief retains natural contours of figures and objects and allows the artwork to be viewed from many angles without distortion of the figures themselves.

Alto-relievo, or high relief is the technique that combines rounded figures with deeper backgrounds. Instead of backgrounds being between a fraction of an inch to few inches deep as they are in bas-relief, they may be a foot to several feet deep in alto-relievo.

 Ralph Crawford