Outstanding Universal Value
OUV is the key concept a site has to comply with to be inscribed in the World Heritage List. This means that the site has a feature that is unique and distinguishes it from any other place on Earth that is relevant for humankind.
In case of the Hortobágy National Park this particular asset is a cultural landscape shaped by pastoral societies for several millennia, maintaining traces of this traditional land use, as well as setting an example for harmonious co-existence of man and nature.
You can reach the official text of the Retrospective Statement of Outstanding Universal Value at the following link http://whc.unesco.org/en/list/474/. Even though it unfortunately contains some mistakes, until correction this is the official version.
Outstanding Universal Value document pdf. format
In case of a cultural landscape, OUV is a complex system of landscape elements let them be of natural or cultural value.