In referring to distance, a click is a military term used to mean 1000 meters or one kilometer. In the American system of measurement, a click is 0.62 miles.
The exact history of the term "click," or "klick," as one more often sees it spelled, is unknown. American soldiers first became familiar with its use during the Vietnam Era. Many believe the term originated in Europe as a sort of shorthand way to say "kilometer." For instance, if a soldier wants to estimate the distance between himself and a certain point, it is easier to say he is two clicks away rather than two kilometers or 2,000 meters from the point.