OU is how British people often write the Open University — a well-known university in the UK built so adults can study from home, first by post and television, later by the internet, without living on a campus. “She’s doing a degree with the OU.” It is a name for that one school, not a general English word you can drop onto any open classroom. You say the two letters. The same letters can mean other things in other places, but this entry is that university.

（英國）開放大學。台灣類似的是「空中大學」，不是同一所。