National parks are protected natural areas that can only be used for human recreation and enjoyment, restricted from development or any form of environmental degradation. National parks are also called reserves that can be declared as such, or owned by the government. Yellowstone National Park in the US is one of the oldest national parks in the world, established under that category in 1872. The International Union for Conservation of Nature (ICUN) and its World Commission on Protected Areas defines national parks under category type 2 protected areas.