I was in Vietnam in Oct.2010, and I noticed that the locals who spoke English used "click" to mean "kilometre", more particularly in the South. E.g.: It is 20 clicks from here = 20 km from here. A search on line reveals that it is indeed a term used, presumably by the Americans originally, in Vietnam, in the days of the Vietnam War (known in Vietnam as the American War). http://www.urbandictionary.com/define.php?term=click I was wondering whether this is American slang, used in the US, or it is army slang, of American origin (hence the Vietnam connection); also, I was wondering why "click". Insight welcome.