Underwear are clothes worn under other clothes, often next to the skin. They keep outer clothes from being made dirty by sweat. They also shape the body and provide support for parts of it, and in cold weather help the wearer to keep warm. Underwear can be used to protect the wearer's modesty, as well as to make them look sexy. Special types of underwear have religious importance. Some items of clothing are made to be worn as underwear, while others such as T-shirts and certain types of shorts can be used both as underwear and as outer clothing. If made of suitable fabric, some types of underwear can serve as nightwear or swimsuits.

Items of underwear commonly worn by women today include brassieres (bras) and panties (also known as knickers), while men wear briefs, trunks, boxer shorts or boxer briefs. Items worn by both women and men include T-shirts, sleeveless shirts, bikini underwear, thongs, T-fronts and G-strings. In countries where the weather is cold, long underwear can be worn to keep warm.

Different words
There are a number of different words for underwear: 'underclothes', 'underclothing'  and 'undergarments' are more formal words.

Female 
In casual situations, underwear may be called 'undies'. In Australia, one may hear underwear being called 'Reg Grundys' or 'Reginalds' (rhyming slang for 'undies'), while in the UK the word 'smalls' is sometimes used. Different types of women's undergarments are known together as 'lingerie' (pronounced LAWN-zhur-ray). They may also be called 'intimate clothing' or simply 'intimates'.

Words for the top half of female lingerie: 'bras', obviously. Note the use of 'teddy' for a one-piece close-fitting nightwear.

Words for the bottom half of female lingerie: pants (US) versus knickers, drawers or panties, but never pants! (UK). 'Briefs' is another possible. 'French knickers' = knickers with frills, looser-fitting. Note the French cache-sex as a prototype 'G-string. Other types of undergarments are spandex shorts common for women who workout.  These shorts are used because it supports the behind and the back for good posture.

Male 
An undershirt is old word for a piece of underwear covering the torso, which has fallen out of usage in the UK, but is still commonly used in North America. Vests is by far the most common term in UK. Underpants  or pants cover the part of the body where the sex organs are, but never drawers. Most common words: shorts  as in boxer shorts for the looser fit. Y-fronts for the tight fit (UK), boxers or briefs used for the same things in Canada and the USA.

These and other words for different types of underwear are set out in the table below. The slang word for a man going without underwear is called free-balling. The slang word fo a bulge in a man's underwear is called mooseknuckle.

Function
Underwear is worn for many reasons. They keep outer clothes from being made dirty by sweat. Men's briefs provide support for the male sex organs, and women's brassieres (bras) do the same thing for their breasts. Some people wear corsets to make their torsos a certain shape. For more support and protection when playing sports, people often put on underwear that fits more tightly for extra support. Men may wear jockstraps and trunks (which are a type of boxer shorts). Women may wear sports bras and pelvic protectors. Sports bras lessens the chance of damage to the ligaments of the chest during vigorous exercises such as jogging.

In countries where the weather is cold, underwear is one more layer of clothing that helps the wearer to keep warm. Underwear can be used to keep the wearer modest – for instance, some women wear camisoles and slips (petticoats) under clothes that are see-through. A camisole is an item of clothing without sleeves that covers the top part of a woman's body, while a slip or petticoat is a kind of skirt that is worn underneath an outer skirt. On the other hand, underwear can also be worn to make a person look more sexy. It is possible to buy underwear made specially to excite another person in a sexual way, such as underwear that can be eaten (it is usually made of small sweets stuck together) and underwear with holes cut into them.

Some items of clothing are designed to be worn as underwear, while others such as T-shirts can be used both as underwear and as outer clothing. Whether underwear can be used as outer clothing depends on a number of things, such as how warm it is indoors and outdoors, what other people in society find acceptable, fashion, and what the law allows. Some types of underwear can be used for sleeping in or as swimsuits, if they are made of suitable fabric.

Religious uses
Underwear can also have religious use:

Judaism. Some types of Jews wear a prayer shawl (a piece of cloth wrapped around the shoulders) called a tallit katan. It has four corners which have tzitzit (fringes) attached to them. Because people who are not Jews do not usually walk about wearing prayer shawls, a Jewish person will often wear a tallit katan beneath a shirt so that it cannot be seen. However, as the shawl is not supposed to touch the skin, an undershirt is worn under it.
Mormonism. Most members of The Church of Jesus Christ of Latter-day Saints (Mormons) wear special temple garments under their clothes after they have gone through special rituals in a temple. They believe that such clothes help them remember the teachings of the temple (sacred covenants), foster modesty, and also shield and protect the wearer.
Sikhism. Sikh men and women believe that they should wear the panj kakaar (five articles of faith) to help them remember their faith. One of the articles is a type of underpants called the kacchera, which are similar to boxer shorts.

Types and styles
The table below sets out types and styles of underwear that are commonfly worn.

Fashions and trends

Designers and retailers
A number of big clothes designers are well known for their underwear collections. Two of these are Calvin Klein and Dolce & Gabbana. There are also companies that make only underwear, such as 2(x)ist, Agent Provocateur, C-IN2, GapBody, Gilly Hicks, Ginch Gonch, La Senza, Fruit of the Loom, Lord, and Victoria's Secret.

Exposed underwear
Although most of the time underwear is kept hidden under other clothes, sometimes it is partly exposed for fashion reasons or to make other people feel sexually excited when they see it. A woman may, for instance, allow the top of her bra to peek out from under her collar, or wear a see-through blouse over it. Some men wear T-shirts underneath partly- or fully-unbuttoned shirts.

A common style among young men is to allow their trousers to sag or droop down below their waists. This fashion is called "sagging". When a person allows his trousers to sag, the waistband or a larger part of his underpants can be seen. A woman wearing trousers which expose the upper back portion of her thong underwear is said to show a "whale tail".

Not wearing underpants

Not wearing underpants under one's outer clothing is known in American slang as "freeballing" for men or "freebuffing" for women. The term "going commando" is also used at times, for both sexes. Certain types of clothes, such as cycling shorts and kilts, are meant to be worn or are traditionally worn without underpants.

Notes