The Open University (OU) is a public research university and the largest university in the United Kingdom by number of students. The majority of the OU's undergraduate students are based in the United Kingdom and principally study off-campus; many of its courses can also be studied anywhere in the world. There are also a number of full-time postgraduate research students based on the 45-hectare (110-acre) university campus at Walton Hall, Milton Keynes, Buckinghamshire, where they use the staff facilities for research, as well as more than 1,000 members of academic and research staff and over 2,500 administrative, operational and support staff.