Place edges side by side, RS facing up: Thread a tapestry needle and bring yarn up through desired stitch; now *go across to the corresponding stitch on opposite side, going into center of that stitch. Come up into center of next stitch on same side; repeat from from *.
See also: Mattress Stitch, backstitch, whip stitch, seam – rows to stitches, Kitchener Stitch – Grafting Knitting, garter seam, flat seam, baste, sew snap tape to front bands, sew snap tape