Athosian term for a period of peak Wraith activity, in which human worlds are subject to particularly intense cullings. Before the Atlantis expedition arrived in the Pegasus Galaxy and awakened the sleeping hives the last Great Holocaust had occurred five generations prior.
The Wraith's typical pattern is to permit population centers to grow larger over the course of several generations, in order to provide a greater amount of sustenance upon which to feed their own massive numbers. After many generations have passed the hives are awakened en masse, and the Wraith return to their feeding grounds -- taking many lives and leaving communities devastated across the galaxy.
But the Wraith are rarely silent altogether, and do attack worlds such as Athos in smaller number and with less frequency during the decades between holocausts -- in order to remind human-populated worlds of their power.
After the Wraith Keeper probed the mind of Marshall Sumner and learned of the rich feeding ground that Earth represents -- and after John Sheppard killed her -- the Wraith were awakened from their long hibernation earlier than was planned, triggering what could be the next great holocaust.
Rising, Part 1 - Teyla tells Sheppard of her people's subjugation to the Wraith, five generations following the last Great Holocaust.
Letters From Pegasus - Sheppard and Teyla witness evidence of a new holocaust first-hand when they helplessly witness a Wraith attack on Orin's planet.