OVA
Definition
An abbreviation for "Original Video Animation". An OV or "original video" is the Japanese term for "straight to video/DVD".
So basically it's an anime series or movie that isn't produced for TV or theaters. Because of this, OVAs can avoid censorship restrictions from TV and other controversies since it's being bought by their core audience.
Example
Chibi Go Nagai World was an OVA series.