What is "buttonhole stitch"

n. reinforcing looped stitch for edges, as around a buttonhole

Buttonhole stitch and the related blanket stitch are hand- sewing stitches used in tailoring, embroidery, and needle lace-making.

Buttonhole stitches catch a loop of the thread on the surface of the fabric and needle is returned to the back of the fabric at a right angle to the original start of the thread. The finished stitch in some ways resembles a letter "L" depending on the spacing of the stitches. For buttonholes the stitches are tightly packed together and for blanket edges they are more spaced out. The properties of this stitch make it ideal for preventing raveling of woven fabric.

Buttonhole stitches are structurally similar to featherstitches.