A reaction video is a genre of short amateur video that captures the reaction of an individual or group of individuals as they encounter a particular text, usually a short media clip.
The first massively popular reaction videos emerged in mid-2007, when thousands of YouTubers uploaded their reactions, often a combination of laughter and retching--to a trailer for a particularly graphic adult film called "2 Girls 1 Cup". The trailer has spawned many reaction videos on the Internet, some of which have attracted many millions of views.
In 2008, another batch of reaction videos emerged around the viral video “Scarlet Takes a Tumble,” a video in which an obese woman sings and dances—and then falls off—a coffee table.
That same year, Twilight fans uploaded reaction videos that captured their affect as they watched the trailer for the film for the first time.