Gusset

Late medieval shirt with gussets in the seams at shoulder, underarm, and hem

In sewing, a gusset is a triangular or rhomboidal piece of fabric inserted into a seam to add breadth or reduce stress from tight-fitting clothing.^[1] Gussets were used at the shoulders, underarms, and hems of traditional shirts and chemises made of rectangular lengths of linen to shape the garments to the body.^[2][3]

Gussets are used in manufacturing of modern tights and pantyhose to add breadth at the crotch seam. As with other synthetic underwear,^[4] these gussets are often made of moisture-wicking breathable fabrics such as cotton, to keep the genital area dry and ventilated.^[5][6][7]

The phrase "don't bust a gusset" (a variation of "don't blow a gasket") is an admonition to calm down; becoming so enraged and inflated that one busted a gusset would imply extreme rage and expansion beyond one's clothing capacity.

Gussets are also used when making three-piece bags, for example in a pattern^[8] for a bag as a long, wide piece which connects the front piece and back piece. By becoming the sides and bottom of the bag, the gusset opens the bag up beyond what simply attaching the front to the back would do. With reference to the dimension of the gusset, the measurements of a flat bottom bag may be quoted as LxWxG.^[9]

Pillows too, are often gusseted, generally an inch or two. The side panels thicken the pillow, allowing more stuffing without bulging.

Gussets are also used in other areas of manufacturing, e.g. bicycle frames employ gussets to add strength and rigidity.

Gusset plates, usually triangular, are often used to join metal plates and can be see in many metal framed constructions.

Special envelopes will also employ a gusset to allow for expansion when containing more than just a few sheets of paper for example.

References

1. Colton, Virginia, ed. (1976). Complete Guide to Modern Sewing. Reader's Digest. ISBN 0-89577-026-1.
2. Burnham, Dorothy, Cut My Cote, Royal Ontario Museum, 1973.
3. Sturm, Mary Mark (1973). Guide to modern clothing (3rd ed.). Webster Division, McGraw-Hill. ISBN 0070622930.
4. US 2826760, Ernest G. Rice, "Combination Stockings and Panty", issued 1958-03-18 
5. "U.S. National Library of Medicine - Vaginal discharge". Retrieved 2013-08-12.
6. US 20030196252 , Sara Blakely, "Two-ply body-smoothing undergarment", issued 2003-10-23
7. Prevention Magazine Editors: The Doctors Book of Home Remedies, Thousands of Tips and Techniques Anyone Can Use to Heal Everyday Health Problems. Bantam, USA 1991, ISBN 0553291564. P. 705, P. 707
8. I taught myself to crochet. No. 7702. Freeport, Illinois: Boye Needle Company. 1975. OCLC 51565050.
9. Ozepac Catalogue