The Collaborative International Dictionary of English v.0.48:

Alto-rilievo \Al"to-ri*lie*vo\, n.; pl. Alto-rilievos. [It.]
   (Sculp.)
   High relief; sculptured work in which the figures project
   more than half their thickness; as, this figure is an
   alto-rilievo or in alto-rilievo.
   [1913 Webster]

   Note: When the figure stands only half out, it is called
         mezzo-rilievo, demi-rilievo, or medium relief; when its
         projection is less than one half, basso-rilievo,
         bas-relief, or low relief.
         [1913 Webster] altostratus