The trimming system is a mechanism built into some sewing machines that automatically trims off excess fabric along the edge during sewing. It consists of one or two knives positioned near the needle. As the machine sews, the knives move and precisely trim the fabric edge just before a stitch is formed. This creates a clean and professionally finished seam that does not fray. This system is a main component of specialized machines known as "overlockers" or "sergers," which are used for seaming and finishing in one step, especially with elastic materials. Some common household sewing machines can also be equipped with a simpler form of trimming, either as a switchable function or using a special accessory presser foot.