IOW is the written short form of the Isle of Wight, a small island off the south coast of England. You see it on envelopes, maps, ferry signs, and in British news. It is not a word you say as one sound; in speech people almost always say “the Isle of Wight,” not the three letters. Though actually, on the internet some people also type IOW for “in other words.” That is chat shorthand, and it is not this sense. And it is not short for Iowa — that American state is IA.