An overlocker, also known as a serger, is a special-purpose machine that produces professionally finished seams, like those found on ready-to-wear garments. It is different from a conventional sewing machine that forms a stitch with a bobbin and top thread. Instead, an overlocker works with loopers and needle threads that form an overlocking stitch. An overlocker uses between two and nearly a dozen threads to encase the raw edge of the fabric with an overcast stitch, while trimming away the seam allowance - all at speeds of up to 1,700 stitches per minute. The primary function of an overlocker is to clean finish a raw edge, giving the project a professional appearance. Many overlocking stitches have built-in stretch, making them the perfect tool for seaming knit fabrics. Additionally, the eyes of the loopers are larger than the eyes of sewing needles and can therefore accommodate thicker decorative threads.

It is important to note that an overlocker does not replace a sewing machine. Its primary function is to finish a raw edge, and it can be used for construction, finishing, or both at the same time. Overlock sewing machines are specialized, but they can save time and give a professional appearance to constructed items. The overlock machine can be used to sew a wide variety of items, from placemats and napkins to sportswear and draperies. The type of overlock machine used will determine the kind of sewing techniques that can be done. The price of the machine depends on the number of threads and loopers, so users should consider the configuration that best fits their needs.