Twitch
Twitch is a website created for the purpose of sharing live video feeds (called "livestreams" or just "streams") on the Internet. Initially intended for a variety of generic uses, Twitch's current incarnation focuses almost entirely on video gaming.
Overview
Twitch's primary purpose is to allow users to record themselves playing video games while others can watch in real-time as they play the game. The service has frequently seen use in high-profile tournaments as to allow interested viewers to spectate games or matches that they ordinarily cannot see live; outside of this, Twitch has also seen use by casual players in order to merely record themselves playing for a public audience, including Let's Plays. Applied uses of Twitch have allowed for viewers to interact with streams, as seen with "Twitch Plays Pokémon", and for viewers to bet on streams, as seen with "Salty Bet"
Streams recorded in Twitch can also be uploaded to YouTube upon their conclusion; similar to YouTube, Twich also offers a partnership programme that allows users to potentially montenise their streams.
Relevance to the Super Smash Bros. series
Given little attention early in its lifetime, Twitch has since become an important aspect of competitive Smash; more recent tournaments have featured the site's services in order to allow outside viewers to watch live matches, an action that previous sites could not easily perform. The sites ability to upload streams to YouTube also allows for those who have missed specific matches to view them later.
Outside of its use in tournaments, some smashers have streamed casual friendlies and money matches with the site's services to general viewers as to show how they play the game regardless of whether or not a tournament is occurring.
Use by Nintendo
Nintendo itself owns a Twitch stream, under the name of "Nintendo". Nintendo's Twitch channel is intended to showcase various trailers of games at specific times and specific events, notably for Nintendo Direct and E3, along with others.
Nintendo's Super Smash Bros. Invitational tournament for [[{{{1}}} (SSB4)|{{{1}}}]] also saw use of Twitch in order to provide a stream for the tournament and its matches.