Klik

A Klik, abbreviated as K, was a measurement of distance used on planet Midnight. (TV: Midnight)

The Vinvocci also used Kliks; when the Tenth Doctor asked how far their ship was from the Naismith Mansion, Addams replied, "50 Kliks". (TV: The End of Time)

Certain Judoon spaceships were capable of moving at speeds of at least 80 million kliks per hour. (TV: Fugitive of the Judoon)

Behind the scenes

 * The term Klik is most likely a future corruption of "Klick", modern-day military slang for kilometre. If so, by the time of the events of Midnight, it seems to have found its way into general use.