backstitch vs sewing stitch

backstitch and sewing stitch both are nouns.

Word	Noun	Adjective	Verb	Adverb
backstitch	Yes	No	Yes	No
sewing stitch	Yes	No	No	No

As nouns, sewing stitch is a hypernym of backstitch; that is, sewing stitch is a word with a broader meaning than backstitch:

backstitch: an overlapping stitch made by starting the next stitch at the middle of the preceding one
sewing stitch: a stitch made with thread and a threaded sewing needle through fabric or leather

Other hypernyms of backstitch include embroidery stitch.

backstitch (noun)	sewing stitch (noun)
an overlapping stitch made by starting the next stitch at the middle of the preceding one	a stitch made with thread and a threaded sewing needle through fabric or leather

backstitch (verb)	sewing stitch (verb)
do backstitches