What is a "gusset"?

A gusset is a triangular or diamond-shaped piece of fabric that is inserted into a garment or other textile item to provide additional space and flexibility, typically in areas where movement is required, such as underarms or crotches of pants. The gusset can also reinforce a garment's seams and help distribute stress points more evenly, making it stronger and more comfortable to wear. It can be made from the same material as the garment or contrasting fabric for decorative purposes. Gussets are commonly found in athletic wear, underwear, and other garments that require greater mobility and durability.