Short for South Korean Telecom1, a Starcraft progaming club. Members and former members include SlayerS'_Boxer, iloveoov, GoRush, Kingdom and Bisu.
It also means SKT1 push in Starcraft: in TvP, the Terran player pushes out with 5-ish marines, a tank, 1 or 2 vultures and research spider mines on the way, against a fast-expanding Protoss.
The purpose of this push is to harass or delay the Protoss's expansion, or force Protoss to build more defenses so that Terran can nullify Protoss's economic advantage or even establish its own.
SKT1 push used to kill every fast-expand Protoss.