En Haut is a classical ballet term meaning “high.” It is a term used to describe another ballet term that is asked to be done in a high position. Most commonly, it is used with “fifth en haut” which is almost always referring to a high fifth position of the arms.
Fifth position en haut is extremely common in classical ballet. It is done very often in class and on stage in performances. It is very often the cliché position of the arms that someone may use to mock a ballerina.
Many ballet terms can be sounded out, at least closely, on the first try, but en haut is one of the big exceptions. It is pronounced “on oh”, though may look like “on hot” to a native English speaker.