The surge in traffic experienced by a web site, usually when something popular or noteworthy is occurring. A flash crowd can be triggered by a news article (the "Slashdot Effect"), interesting events in the world (Traffic received by voter.com during the US presidential election in 2000), or a download (the release of HelixCode).

Flash crowds usually cause a denial of service of the origin server, unless it has either sufficient bandwidth on the first mile, or uses a content delivery network to absorb the crowd.

flarp = F = flat

flash crowd

Larry Niven's 1973 SF short story "Flash Crowd" predicted that one consequence of cheap teleportation would be huge crowds materializing almost instantly at the sites of interesting news stories. Twenty years later the term passed into common use on the Internet to describe exponential spikes in website or server usage when one passes a certain threshold of popular interest (what this does to the server may also be called slashdot effect).

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.