km is the short written form of kilometre or kilometres, the metric unit of distance. One kilometre is 1,000 metres — about a long walk, or a bit more than half a mile. You see km on road signs, maps, running apps, and science work. When you read it aloud, say “kilometre” or “kilometres,” not the letters K-M, except when you are spelling it out. In American spelling you will also meet kilometer. Though actually, in everyday Taiwan life people often say the Chinese word and still write km, especially on signs and in sports. In scientific writing there is no period: km, not km. For speed you will see km/h — kilometres per hour.