An establishment that earns its money by charging exorbitant "cover" fees to those wishing to enter and by selling overpriced, watered-down beverages (alcoholic and otherwise). Within the building, the only "services" provided by the business itself are the presence of a (normally obnoxiously overconfident) DJ, a sound system suitable for a 50,000-person stadium being used solely to destroy the patrons' eardrums and convey the "music" to them exclusively by vibrating it into them via the floors and walls, a dancing surface, and possibly a coat check service and a random sprinkling of small, wobbly tables and uncomfortable chairs.
Males normally visit these establishments with hopes of meeting one or more females to copulate with, either in the bathroom right there, or at home later that evening. Females normally visit these establishments with hopes of entertaining many such propositions and shooting them down mercilessly. Because of this behavior, nightclubs are commonly referred to as "meat markets", even by the establishments themselves.
Nightclubs encourage this behavior because everything else people try to do in these clubs (consuming illegal drugs, sell illegal drugs, and so on) are illegal, and will cause local law enforcement to execute a raid, thus closing down the establishment at least for a few days.
Nightclubs make themselves more popular by first producing the illusion of popularity, which then self-feeds until the club actually is popular. They do this by forcing would-be patrons to stand in an intolerably long line outside the club. This is an important detail -- this line is always outside the club, always within earshot of the sounds within, and always within view of the public -- because this creates the illusion of popularity. People naturally assume there must be some reason lots of other people are queued up, and thus the illusion of popularity becomes real.
Passage into a nightclub is effected by appeasing a creature known as a "bouncer". These creatures are typically large, antisocial, and unfriendly. They enforce a disturbing social structure by permitting those willing to bribe them with cash to move to the head of the line or skip past it entirely. The structure simultaneously punishes those who are attempting to follow all the rules (including self-defeating dress codes that usually require such goofy things as dress shoes even though the dancing within requires sneakers) but are not willing to bribe their way in.
The social structure is further perpetuated by the biased, subjective nature of the selection process -- some people (almost always male) who have dressed appropriately are turned away regardless, while others (usually female, particularly if they have large breasts or are flirtatious) are granted immediate entrance, sometimes even without paying a cover fee.
Within the club, above the deafening noises, people attempt to dance and flirt and have sex with each other. The dancing is almost always horrible, the people are invariably clumsy, and the hearing loss is nearly immediate and usually permanent.
Any attempt by a male to attract a female for copulation purposes is immediately rejected harshly. Because females only visit these clubs in groups, they are present in large numbers to ridicule anyone who attempts to hit on any of them. This discourages further attempts, leading to disgruntled male patrons' increased consumption of alcohol, which in turn leads to potentially dangerous behavior, including rioting and violence.