Stitch in the ditch
A machine stitching technique where you sew directly into the seam line (the ditch) to secure an underlayer invisibly.
Where it is used
Stitching Waistband in the Ditch
p. 9- From the right side of the dress, sew precisely in the groove (stitch-in-the-ditch) between the waistband and the skirt to secure the inner waistband on the reverse side.

17.10. Topstitching waistband ditch
p. 29- Sew a topstitch along the seam where the outer waistband is attached, stitching right in the seam ditch. Remove the basting threads.

Step 14: Finishing Inner Waistband
p. 4- Finish the open edge of the inner side of the waistband by either binding or pressing 10mm to the inside. Then stitch the inner part of the waistband to the waist in the ditch or 1-2mm from the edge on the right side.
