What's an OAV (or OVA)?
They're abbreviations of Original Animated Video and Original Video Animation respectively. They refer to direct to video releases in Japan. This means that they were released onto video tape (now DVD) instead of being shown on TV or in a theater. They're a middle ground between TV and movies in almost every respect. They tend to be longer than most movies, but shorter than most TV shows. They also usually run a short series (3-5 episodes), though one shots are relatively common too. They usually have a higher budger than TV shows, but a lower budget than movies.
OAV's hit their peak in the early nineties. There aren't nearly as many being released now.
- WikiPedia: ↗OVA