low relief vs sculptural relief

low relief and sculptural relief both are nouns.

Word	Noun	Adjective	Verb	Adverb
low relief	Yes	No	No	No
sculptural relief	Yes	No	No	No

As nouns, sculptural relief is a hypernym of low relief; that is, sculptural relief is a word with a broader meaning than low relief:

low relief: a sculptural relief in which forms extend only slightly from the background; no figures are undercut
sculptural relief: sculpture consisting of shapes carved on a surface so as to stand out from the surrounding background

Other hypernyms of low relief include embossment, relief, relievo, rilievo.

low relief (noun)	sculptural relief (noun)
a sculptural relief in which forms extend only slightly from the background; no figures are undercut	sculpture consisting of shapes carved on a surface so as to stand out from the surrounding background