Slashdot effect
A small site gets linked from a large forum and collapses under the traffic within minutes. Named after Slashdot, which was the first to do it regularly.
Slashdot launched in 1997 under Rob Malda and gathered enough technically-minded readers that a front-page link could aim tens of thousands of visitors at an Apache server sitting under somebody's desk. The result was timeouts, exhausted database connection pools and a site that was down at precisely the moment it got attention. The phenomenon is now usually called the hug of death and is just as likely to come from Hacker News, Reddit or a viral thread. The countermeasures are what they always were: cache everything you can, serve static HTML instead of generating a page per visit, and put a CDN in front. The joke is that a well-built site never notices.