The Kop is a generic reference to main standing area in a football stadium, named after the South African mountain Spion Kop, scene of a battle in the Second Boer War.
Many English grounds have a Kop, though the most famous one is at Anfield, home of Liverpool, which is the only club to give their stand the official name of 'The Kop'. The name sticks to this day both officially and spiritually, even though the stand itself became all-seater in the 1990s.