A station in West London on the Central Line. It is in Travelcard Zone 5. A station on the Great Western line (a track of which still runs alongside) was built in 1907: the current station was opened 21 November 1948.
RAF Northolt is actually in the Ruislip area - the name dates from the period of construction, when the whole area was given the name.
The Wikipedia page is [1] and the TfL is [2].
See also Northolt Park Station