One-click is the distance of one kilometer, especially in the US military jargon. The origin of the word in this context is unknown, a theory leads it to a shortening or practice-speaking grind of the word kilometer back. The use in the Vietnam War in the 1960s was popular. In English-speaking countries it is sometimes also called click, klik or clic.
If a click is spoken, it can also be an unspecified short distance.
Another meaning is the click. This additional military term corresponds to an arc minute when setting a target telescope. Edit sourcetext
wiki