Outer Mongolia

Outer Mongolia is a region located on the Asian continent of Earth. The name is also a slang term which is used to describe something that is impossible to achieve.

After arriving in 1930 via the Guardian of Forever to await the arrival of Dr. Leonard H. McCoy, James T. Kirk referred to as Outer Mongolia as one of the possible locations that McCoy could appear, as if to underline the impossibility of finding him. (TOS episode: "The City on the Edge of Forever"; novel: Crucible: The Fire and the Rose).