A nightclub (often shortened to club) is an entertainment venue which does its primary business after dark. A nightclub is usually distinguished from other forms of drinking and entertainment establishments, such as bars, pubs or taverns, by the inclusion of a dance floor. In most other languages, nightclubs are referred to as "discos" or "discothèques" (French: discothèque; German: Disko or Diskothek; Spanish: Discoteca). In Japanese , disuko refers to an older, smaller, less fashionable venue; while kurabu refers to a more recent, larger, more popular venue. The term night is often used to refer to an event hosted within a nightclub, such as "retro music night." A dance area too small to be considered a night club, but which has a bar, music and lighting effects, is occasionally referred to as a disco bar.
Nightclubs are associated with socializing and music and are usually distinguished from other forms of drinking establishment, such as a bar, pub or tavern, by the inclusion of a dance floor, although a club may also feature other forms of entertainment, possibly in forms unsuitable for minors, such as podium dancers, a floor show or strippers (see strip club). Music may be live or mixed by a DJ and is often amplified using a PA system, and can range from blues, jazz, country, disco, hip-hop, rock and metal to electronic music styles such as house, techno, trance, drum and bass and alternative electronic. Most clubs or club nights have a specific musical theme and generally cater to fans of a few particular music genres.

Gatherings in clubs at night that primarily involve music mixed by a DJ involve dancing and in most cases alcohol. Illegal use of recreational drugs such as ecstasy are commonplace in many modern clubs featuring electronic dance music.[citation needed] Clubs are often advertised by the handing out of flyers on the street, in record shops, and at other clubs and events, these are often highly decorative and eye-catching.

Nightclubs often feature lighting and other effects: flashing lights of many colors, moving light beams, laser light shows and smoke machines. One common item is a disco ball: a rotating football-sized spheroid at the ceiling, covered with many small flat mirrors, with a light beam directed on it; the reflections form a multitude of moving light spots on the floor and on the people. Some nightclubs will throw foam parties where the dance floor is filled with soap suds.

Source: http://en.wikipedia.org