Serpentine is a common utility stitch on machines. It looks like an S . Basically it is a straight stitch that waves back and forth. If you Google "machine serpentine stitch" and click on "images" you should find some examples.
On most machines you can adjust the stitch length and width of the serpentine to suit your preference. On my Bernina 1230 it's stitch #3. I leave it at full width and lengthen the stitch to about 1.5.