Jmat has pretty much hit the nail on the head, except for some minor details. 東 is a Traditional Chinese character and 东 is a Simplified Chinese character. Simplified Chinese was created in the 1950s. Today, it is only used in Mainland China and Singapore. Hong Kong and Taiwan still use Traditional Chinese to this day. The only purpose of Simplified Chinese is to make Chinese easier to write, and that's literally the only difference between Simplified and Traditional Chinese. They are just 2 different writing standards. Sometimes people ask me whether I *speak* Simplified Chinese or Traditional Chinese, and that's not a valid question. I speak Mandarin, and I *write* Simplified Chinese. Personally, I cannot write Traditional Chinese, but I have little trouble reading it. In terms of interchangeability, I don't think I have an answer for you, because the question itself doesn't make a lot of sense. Let me explain why. For example, the word "color" is spelled "colour" in the UK and "color" in the US. Kind of like 東 and 东, "color" and "colour" are just 2 different ways to write the same word. So do you think "color" and "colour" are interchangeable? In my opinion, the question is meaningless, because no one will ever attempt to "interchange" them. American people will always write "color" and British people will always write "colour", but everyone can recognize both "color" and "colour".