What is the primary function of a serger in garment construction?

A serger, also called an overlocker, is a specialised sewing machine designed to finish the raw edges of fabric. It uses multiple threads (typically three or four) to simultaneously trim the seam allowance, stitch the seam, and encase the raw edge in thread. This prevents the fabric from fraying and unravelling, producing a neat, professional finish similar to what is seen on commercially manufactured clothing.

To finish seams and prevent fraying is the correct answer because this is the serger's primary and defining function. While a regular sewing machine can construct seams, it cannot efficiently finish raw edges the way a serger can.

Sewing heavy fabrics is better served by an industrial or heavy-duty sewing machine, not specifically a serger. Creating buttonholes requires a buttonhole foot or a specialised buttonhole machine. Sewing straight lines is a basic function of any standard sewing machine. None of these describes the serger's distinctive role in garment construction.