Serge

An overlock stitch worked around the raw cut edge of fabric so the edge cannot fray or unravel. On knits it is the standard way to finish a seam allowance, and it stretches with the fabric instead of snapping. Serging is quick and cheap, which is why it appears on nearly every garment in the catalogue; the alternative, a fully enclosed or bound seam, is a premium feature. Note that the same word also names a twill-woven suiting fabric, an unrelated meaning you will meet in woven-goods listings.