Often a pattern will instruct you to stay-stitch an area before sewing a seam.  This is a line of stitching to stabilize an area before clipping into the seam allowance to make construction easier.  This is typically done on an inside curve such an a neckline (before adding a collar), or at an inside corner to open it when fitting pieces together.  The stitches are shorter than construction stitches and are placed just inside the seam line (usually 1/8" or less).