In sewing and dressmaking, a ruffle, frill, or furbelow is a strip of fabric, lace or ribbon tightly gathered or pleated on one edge and applied to a garment, bedding, or other textile as a form of trimming.

Ruffles can be made from a single layer of fabric (which may need a hem) or a doubled layer. Plain ruffles are usually cut on the straight grain.

Ruffles may be gathered by using a gathering stitch, or by passing the fabric through a mechanical ruffler, which is an attachment available for some sewing machines.

A flounce is a particular type of fabric manipulation that creates a similar look but with less bulk. The term derives from earlier terms of frounce or fronce. A wavy effect is achieved without gathers or pleats by cutting a curved (or even circular) strip of fabric and applying the inner or shorter edge to the garment. The depth of the curve as well as the width of the fabric determines the depth of the flounce. A godet is a circle wedge that can be inserted into a flounce to further deepen the outer floating wave without adding additional bulk at the point of attachment to the body of the garment, such as at the hemline, collar or sleeve.

Ruffles appeared at the draw-string necklines of full chemises in the 15th century and evolved into the separately-constructed ruff of the 16th century. Ruffles and flounces remained a fashionable form of trim, off-and-on, into modern times.