A LAN party is a temporary, sometimes spontaneous gathering of people together with their computers, which they network together primarily for the purpose of playing multiplayer computer games.
These LANs come in various sizes, from the very small (2 people) to the very large (4000+ people). Small parties can form spontaneously, but large ones usually require a fair amount of planning and preparation on the part of the organizing team.
Many parties offer various tournaments, competing in such games as Quake III or Warcraft III, sometimes awarding prizes to the winners, as well as counting for standings in national and international gaming leagues, such as the WWCL. There are regular events, such as QuakeCon, in which the very best players from around the world compete against one another, much like in popular sports.
The duration of the event is not standardized; many organized parties last for a weekend, while there have also been longer and shorter parties. In particular, small, spontaneous parties often last for only minutes to hours.
Big LAN parties often offer a quiet place to sleep, showers, catering, alternative entertainment (such as music) and a dedicated support crew, as well as a professionally managed network including an uplink to the Internet.
Gaming clans, groups of gamers that often play in team games such as Counter-Strike, often use these gatherings to meet one another, since they typically play together over the Internet between parties with little real-world contact. Their goal is often to win tournaments.
While being the minority and usually discouraged or forbidden by the party organization, some attendees also use these parties primarily for the purpose of piracy of intellectual property.
There are also other kinds of parties where temporary LANs are built, but which are not commonly referred to as a "LAN party" alone; amongst these are demo parties such as Assembly, hacker conventions such as DEF CON, and freestyle events such as the Burning Man.