A chunk of lithosphere on the west coast of Central America, identified by plate tectonics. The Cocos plate pushes against the heavier Carribean plate and subducts beneath it. It also forces the Caribbean plate against the large North Marican plate to the north. The interaction of these plates cause earthquakes and volcanism in Nicaragua and Guatemala. It is also in contact with the Nazca Plate.
It's thought to be a fragment of the ancient Farallon plate, which split off when the Farallon plate subducted beneath the North American plate.