Klick is a common military term meaning kilometer when referring to distance. Its use became popular among US soldiers in Vietnam during the 1960s, although veterans of the war recall its usage as early as the 1950s. The term is of unknown origin. It is likely to be an example of condensedpronunciation or contraction of the term kilometer, although other theories exist.
Either a kilometre or a kilometre per hour ("kilometer" for Americans) depending on context. Pronounced as "click" but always written with an initial 'k'.
Common in Canada. In the US it's strongly associated with the military.
See k which can also be used for "kilometre" but not for "kilometre per hour".