Made-for-home-video-market animation (i.e. no prior TV or theatrical release). Usually anime.
Can't believe this acronym hasn't already been expanded on the Wiki. I always called it OVA too. Anyhow - if it's long and pretty but comes in two or three chunks, it's an OVA. If it comes in many many smaller chunks it's a series, and if there's only a single huge chunk and it blows chunks, then it's a movie. --Vitenka (rule of thumb)
With western films (since we only get short series on TV release, rather than video-only, AFAIK) 'straight to video' is really rather a derogatory term - and implies it was bad. I'm given to understand that this simply isn't the case in Japan (and, indeed, might be diametrically wrong). -- TheInquisitor
It's more fair to compare OVAs to pilot episodes. Longer than a normal episode of a series, usually with the best money and plot they can throw at it, to try to hook people and get the cash they need to make the series proper. Whereas here, StraightToVideo? means a movie - usually a sequel - which didn't test highly enough to make it to the cinema. --Vitenka
You get a reasonable number of OAVs which have between 2 and 6 episodes and are self-contained stories rather than pilots for series. They (used to) tend to have higher animation quality than typical longer-running TV anime series, but this is less noticeable with certain TV anime getting very high quality recently. --AlexChurchill