WHAT IS IT?
A whipstitch is a quick hand stitch that is used to “whip” two edges together. This stitch is visible, so it’s usually done on the inside of the garment or other places where it will not show from the right side.
Whipstitch to close zipper tape
WHEN DO YOU USE IT?
Use a whipstitch when you have two edges that need to be joined together quickly. Whipstitching can be used as temporary stitching as well. When inserting a zipper in a seam that is sewn both above and below the zipper opening, whipstitch the edges of the zipper tape together before inserting the zipper. (See lapped zipper page link for more.)
HOW TO SEW A WHIPSTITCH
Thread a handsewing needle with a single thread. Take a stitch through both sides to join at a right angle to the edge.
Repeat all the way across the edges. Sewing at a right angle makes the stitches slant as they enclose the edge.
Source : The Sewtionary An A to Z Guide to 101 Sewing Techniques + Definitions
About the Author : Tasia ST. Germaine