Undergarments or underwear are items of clothing worn beneath outer clothes, usually in direct contact with the skin, although they may comprise more than a single layer. They serve to keep outer garments from being soiled or damaged by bodily excretions, to lessen the friction of outerwear against the skin, to shape the body, and to provide conceallment or support for parts of it. In cold weather, long underwear is sometimes worn to provide additional warmth. Special types of undergarments have religious significance. Some items of clothing are designed as undergarments, while others, such as T-shirts and certain types of shorts, are appropriate both as undergarments and as outer clothing. If made of suitable material or textile, some undergarments can serve as nightwear or swimsuits, and some are intended for sexual attraction or visual appeal.

Undergarments are generally of two types, those that are worn to cover the torso and those that are worn to cover the waist and legs, although there are also garments which cover both. Different styles of undergarments are generally worn by females and males. Undergarments commonly worn by females today include bras and panties (knickers in British English), while males often wear classic briefs, boxer briefs, or boxer shorts. Items worn by both sexes include T-shirts, sleeveless shirts (also called singlets or tank tops), bikini underpants, thongs, G-strings and T-fronts.

Terminology

Undergarments are known by a number of terms. Underclothes, underclothing and underwear are formal terms, while undergarments may be more casually called, in Australia, Reg Grundys (rhyming slang for undies) and Reginalds, and, in the United Kingdom, smalls (from the earlier smallclothes) and (historically) unmentionables. In the United States, women's underwear may be known as delicates due to the recommended washing machine cycle or because they are, simply put, delicate.

Women's undergarments collectively are also called lingerie. They also are called intimate clothing and intimates.

An undershirt (vest in the United Kingdom) is a piece of underwear covering the torso, while underpants (pants in the United Kingdom), drawers, and undershorts cover the genitals and buttocks. Terms for specific undergarments are shown in the table below.

Not wearing underpants under outer clothing is known in American slang as going commando,free-balling for males, or free-buffing for females. The act of a woman not wearing a bra is sometimes referred to as freeboobing.

Function

Underwear is worn for a variety of reasons. They keep outer garments from being soiled by perspiration, urine, semen, pre-seminal fluid, feces, vaginal discharge, and menstrual blood.Women's brassieres provide support for the breasts, and men's briefs serve the same function for the male genitalia. A corset may be worn as a foundation garment to alter a woman's body shape. For additional support and protection when playing sports, men often wear more tightly fitting underwear, including jockstraps and jockstraps with cup pocket and protective cup. Women may wear sports bras which provide greater support, thus increasing comfort and reducing the chance of damage to the ligaments of the chest during high-impact exercises such as jogging.

In cold climates, underwear may constitute an additional layer of clothing helping to keep the wearer warm. Underwear may also be used to preserve the wearer's modesty – for instance, some women wear camisoles and slips (petticoats) under clothes that are sheer. Conversely, some types of underwear can be worn for sexual titillation, such as edible underwear or crotchless panties.

Undergarments are worn for insulation under space suits and dry suits. In the case of dry suits, the insulation value of the undergarments is selected to match the expected water temperature and the level of activity for the planned dive or water activity.

Some items of clothing are designed exclusively as underwear, while others such as T-shirts and certain types of shorts are suitable both as underwear and as outer clothing. The suitability of underwear as outer clothing is, apart from the indoor or outdoor climate, largely dependent on societal norms, fashion, and the requirements of the law. If made of suitable material, some underwear can serve as nightwear or swimsuits.

Religious functions

Undergarments can also have religious significance:

• Judaism. To conform with societal dress codes, the tallit katan is often worn beneath the shirt.

• Mormonism. Following their endowment in a temple, Mormons wear special temple garments which help them to remember the teachings of the temple.

• Sikhism. One of the five articles of faith (panj kakaar) worn by Sikh men and women is a certain style of underpants similar to boxer shorts and known as the kacchera.

• Zoroastrianism. Zoroastrians wear an undershirt called a Sedreh that is fastened with a sacred girdle around the waist known as a Kushti.