Kush refers to a subset of strains of Cannabis indica. The origins of Kush Cannabis are from landrace plants mainly in Afghanistan, Northern Pakistan and North-Western India with the name coming from the Hindu Kush mountain range. "Hindu Kush" strains of Cannabis were brought to the United States in the mid-to-late 1970s and continue to be available there to the present day.
Many cite Pink Kush as the original Kush strain created by GW Pharmaceuticals and UBC Professor David Suzuki, who created a super strain by creating a tetraploid plant that was bigger and stronger than most cannabis plants. Pink Kush than found its way down the West Coast of the U.S. and bred the Kush strains most know (OG Kush being the most popular).