A speedrun is a play-through, or recording thereof, of a whole video game or a selected part of it (such as a single level) performed with the intent of completing it as fast as possible, optionally under certain prerequisites, mainly for the purposes of entertainment and competition. The term is a compound of the words speed and run (as in "running" through a game, referring to the playing of a game). There's also a website for uploading recorded speedrun videos at http://www.speedrun.com/
Commonly, speedruns are recorded on either media such as DVDs (predominantly when games on consoles are concerned), or as digital files, by the people ("players") who make them, for entertainment, time refinement, or verifiability purposes.
Entertainment has traditionally been the reason for the creation of speedruns, as the phenomenon was originally devised by enthusiasts who began comparing each other's playing skills via movies exchanged over the Internet, while verifiability stems from the necessity to provide evidence that one's playthrough went by the typical or game-specific speedrun rules and thus counts as a valid attempt to beat the record.
In order to attain the highest possible quality of play in a speedrun, the author usually has to look at and think about the game differently from the way that most casual gamers would. It is usually required that speedruns be planned out carefully before they are attempted; this need stems from the complexity of the separate areas in which the gameplay takes place. Additionally, games and their physics engines are not flawless and will allow the runner to do unexpected things that could save time. Despite their inherent differences, they seem to share a lot of common traits in this context, such as the ability to disjunct the common sequence of events in a game and thus skip entire parts of it—the act of sequence breaking—and the ability to use programming errors, or glitches, to one's advantage.
Some games are considered to be ideal specimen for fast completion purposes and have online communities dedicated to them, which provide (or have provided) a highly active platform for discussing the speedrunning of one or more of these particular games.
While speedrunning initially started out as a small project, initiated by a few enthusiasts who shared their demos online, it has since become a phenomenon that encompasses several active websites and an increasingly expansive assortment of speedrun videos that are freely and widely circulated on the Internet.