The buttocks are the two masses of muscle (the gluteus maximus, gluteus medius and gluteus minimus) and fat covering the posterior aspect of the human pelvis. The anatomical Latin name for the buttocks is nates (pronounced /'neɪti:z/ in English).
Although gluteus maximus is one of the biggest and strongest muscles in the human body, between a third (in children and men) and half (in women) of the buttocks mass is actually fat. The two hemisphere-shaped masses of the buttocks are called cheeks. The vertical crack between the cheeks is properly called gluteal cleft or natal cleft. The horizontal fold where the buttocks meet the legs is called gluteal sulcus. Above the buttocks, at the lower back, is the sacral triangle.
Viewing a nice pair of buttocks of the desired gender is sexually arousing for many, but not all. The sexual aesthetics of the buttocks vary greatly from culture to culture, with some finding leaner buttocks attractive while some find extremely fatty buttocks (steatopygia) desirable.
A particularly rounded (usually female) buttocks is called a bubble butt.
Some clothing is designed specifically to show off the buttocks, like thong underwear, or to expose them (for punishment in BDSM), or has a butt flap to allow baring only the bottom with a simple gesture (as for hygiene).
In many cultures, corporal punishment is traditionally delivered on the buttocks (it is then called spanking, though in British English this is generally said only when applied by hand, not with an implement such as a strap, birch or cane).
This is especially true for lighter punishment and domestic discipline on children (and in some cultures, on wives). Different reasons have been put forward to explain the preference for this anatomical target:
- While there are many nerve endings in the area (ensuring sufficient pain), there is relatively little risk of the spankee sustaining long-term injury since internal and other vulnerable organs are are unlikely to be affected.
- The buttocks are considered shameful, and having them bared or being made to disrobe them for punishment is added humiliation.
Spankophiles call the lower inner portion of the buttocks the "sweet spot", because getting spanked there feels especially good. The suspected reason for this is probably because this region is fed by the same nerve group that is shared by the genitals.
As buttocks are an object of both shame and fascination, it is not surprising that there are rather a lot of colloquial terms, euphemistic, ironic or other, to refer to them. These include :
- butt, backside, behind and its derivatives (as hiney, hind-quarter, or hind), bottom (bottie and botty), derrière, posterior, rear or rear-end - all strictly positional descriptions, as is the inaccurate use of rump (as in 'rump roast', after a 'hot' spanking), thighs, upper legs
- analogous are: aft, stern and poop, naval in origin; tail (even as there is a tail-bone) and tail-end
- arse (British English) or ass (American English), and (butt-)hole - a pars pro toto (strictly only the actual anal region)
- bum - of uncertain origin
- buns - a shape-metaphor
- cheeks, a shape-metaphor within human anatomy, but also used in the singular: left cheek and right cheek; especially nether cheeks
- seat (of the trousers; or metaphorically)
- seat of honor, seat of learning, seat of education (humorously)
- the bare (referring to the bare buttocks)
- glutes (the group of the three large muscles of each buttock - common term in bodybuilding)
- tush, tushy (from Yiddish/Hebrew "tuchis" or "tochis" meaning "under" or "beneath")
- fanny, American English only, means vagina in British English.
- fundament, the part of the body upon which one sits; the buttocks; specifically, the anus.
- booty (especially female)
- bundas (derived from Portuguese)
- badonkadonk (referring to big but firm female buttocks)
- hindquarter(s) (metaphorically)
A callipygian (from Greek kallipygosis) is a person who has beautiful buttocks.
 Types of buttocks
The following drawing from A Trendsettin Legacy shows different "types" of buttocks.
 See also
- Butterfly buttocks
- "Buttocks" in other languages
- Buttock on Wikipedia
- Female Buttocks drawing tutorial (in Russian)