A klick is military slang for a kilometer, which equals 1,000 meters or 0.62 mile. The term came into wide use among U.S. troops in Vietnam during the 1960s though its exact origin is unknown.
Neither the term "klick" nor "click," a commonly used alternate spelling, is contained in the Department of Defense Dictionary. The "DOD Dictionary of Military and Associated Terms" lists all definitions, acronyms and abbreviations approved by the Joint Education and Doctrine Division. Approved military acronyms and terms typically serve a utilitarian purpose, such as more easily identifying alphabet letters and enhancing communication over the radio. Military slang typically reflects the pop culture and environmental circumstances of the time.