low relief vs embossment

low relief and embossment both are nouns.

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

As nouns, embossment is a hypernym of low relief; that is, embossment 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
embossment: sculpture consisting of shapes carved on a surface so as to stand out from the surrounding background

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

low relief (noun)	embossment (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
	an impression produced by pressure or printing