开 is Simplified Chinese, a revised way of Chinese writing. About 3 decades ago in all Mandarin speaking countries, the glyph used to be written as 開, with a door "門", which makes perfect sense. That is what we call Traditional Chinese. The glyph is still in use in countries such as Hong Kong, Taiwan and Japan.
Open can be written as '开' in Chinese, which is pronounced as 'kai'. It also can be written in other characters.