Back Stitch Loop Knot
A hand-sewing knot used to end a stitched thread. When the last stitch has been completed, make a Back Stitch, approximately 1/8" behind the last stitch, bringing the needle back through the fabric to form a loop on top of the previous stitch. Pull the Back Stitch up so that the loop is on the top of the work. Put the needle through the loop and pull thread tightly. Trim the excess thread.
Quilter's Complete Guide, p 22