Underground station, and former railway station, the northern terminus of the High Barnet branch on the Northern Line in Travelcard Zone 5.
It was opened by the Great Northern Railway on 1 April 1872, on the site of the Barnet Fair. It was transferred to London Underground as part of the "Northern Heights", underground services beginning 14 April 1940. from the pre-LT era.
More information on the Wikipedia page [1]. The TfL page is [2].