Underwear, is clothing worn beneath other clothing, generally adjacent to the skin. Underwear usually covers parts of the torso such as the genitals and buttocks (underpants, e.g. briefs or panties), or female breasts (e.g. bra) though unisexually it can also induce an undershirt like a singlet or t-shirt. Socks, for example, are not called underwear. Swimwear is technically similar to underwear, but also not called underwear because it is not designed to be worn beneath other clothing.
Since large groups of English speaking males stopped wearing undershirts, the word "underwear" started meaning just underpants and no longer upper body garments, except in the combination "women's underwear". A colloquial term for underwear (in the sense of underpants, especially among children and young adults) is undies. In most places, the word "undies" is unisex, but in Australian and New Zealand English it has a strong male bias. In British English, the word pants refers to (mostly male) underwear in the sense of underpants.
Not wearing any underwear under one's outer clothing is known as going commando.
 Underwear in spanking
 Exposure of underwear/buttocks
It is common in spanking scenes, for the spankee to be required to expose his or her underwear, or to have it moved or removed, or both. This affords access to the bottom, allowing a bare bottom spanking. It also contributes to the embarrassment/humiliation factor. In the context of domestic spanking, some people think that a spanking is best carried out over the underwear. This is supposed to be an ideal compromise between not humiliating the child or teenager being spanked and still allowing the spanking to be sufficiently felt, because while jeans estimatedly absorb about 70% of a spanking's impact, underpants absorb only 10-20%.
 Special underwear
In some cases a spankee will be required to wear special underwear for spanking purposes. In Lurking Dragon's stories (e.g. Collegegirl) the girl to be punished is sometimes made to wear particularly "childish" underwear, of the kind that is normally worn by very small children, for their cuteness factor and also for extra punishment through humiliation. In Rejuve Universe, there is also special punishment underwear that stings, known as pain-ties and bee-riefs.
Another option for punishment underwear is the kind that permits special access to the bare bottom, e.g. via a seat flap (drop seat), via a lengthwise slit as in vintage open drawers or simply simply being seat-less like a jockstrap.
In urtication (e.g. BDSM play), one way of applying stinging nettles to the skin is by putting them inside the person's underwear. The spanking video And for You I Will Come as Well from Lupus Pictures shows three young girls enduring this type of punishment.
- How to Spank by Paul J Preston