A criss-cross embroidery stitch used on sheer materials for filling in spaces, worked on the reverse side so as to show through in a shadowy way with an outline resembling a backstitch.
Definition of shadow stitch in US English:
shadow stitch
noun
A crisscross embroidery stitch used on sheer materials for filling in spaces, worked on the reverse side so as to show through in a shadowy way with an outline resembling a backstitch.