Bicycle shorts

Cycling shorts (also known as bike shorts, bicycling shorts, chamois, knicks, or spats) are short, skin-tight legwear designed to improve comfort and efficiency while cycling. They:

Historically, cycling shorts were made of knit black wool, which hides oil and grease stains, with a chamois leather padding inside the shorts in the crotch area, which reduces chafing from the bicycle saddle. Modern cycling shorts are often made of spandex (Lycra) with a synthetic chamois which acts as an elastic interface between the cyclist's body and the saddle, and are produced in a variety of shapes and styles to suit the needs of different riders. On some cycling shorts different materials are often placed on different parts of the shorts to take advantage of each materials benefit providing a very efficicent cycling short. For example, the patterns used for the chamois on women's cycling shorts tend to be quite different from those used for men's. The hem of each leg is usually lined with elastic and/or silicone that clings to the skin, keeping it in a fixed position. These shorts made from several panels (or cuts of fabric) fit better and are more beneficial, especially for racers, but cost more.

Short-legged elastic tights commonly worn as street wear, under girls skirts and dresses, for gymnastics and ballet practice, or under athletic and running shorts are sometimes also referred to as "bike shorts", but they are typically simpler and lighter garments than those worn by cyclists and generally lack the chamois or faux-chamois lining.

Bib shorts are cycling shorts that are held up by a bib (integral suspenders/braces) instead of an elastic waistband. Pro and serious riders tend to prefer bib shorts over non-bib shorts, due to the discomfort that often occurs with an elastic waistband, such as tightness (digging into skin) and chafing. The bib part of the short is often made of spandex and polyester with large sections of netting to help keep the rider cool.

The idea of modern bib shorts was a development from the braces (UK) or suspenders (US) that cyclists once used to hold up old-fashioned wool shorts, which had a tendency to become loose and heavy from riders' sweat (the use of braces/suspenders meant the shorts could be held up without an uncomfortably tight waistband). Bib shorts are well-suited to tall riders and riders with protruding stomachs because regular shorts can tend to fall down in the back while riding.

These shorts typically are more loose than bib shorts but still not baggy. This is because they are focused more on protecting the rider during falls and are not as focused on aerodynamic efficiency. The position of the padding is a little different because mountain bikers have a more upright stance when riding. These shorts are different from baggy shorts as they are used by hardcore cyclists who still need the protection with a good padding, which the baggy shorts do not have.

...
Wikipedia