A. JAV stands for Japanese Adult Video. In almost all cases, unless otherwise stated these videos will be censored (to varying degrees) with what is called a "mosaic". In Japan, the law states genitals can not be clearly shown. Other major countries have similar restrictions - often even more restrictive than Japan.
Some may ask "Then why do people like JAV?". Well, I suppose it's an acquired taste. Of course, many of us just have "a thing" for cute Japanese girls, which you can't easily find in adult video outside of Japan. Also, the Japanese culture is rather unique and it shows in the content of many of their movies. Finally, JAV does not often have that "fake" feel that other porn does. No funky porn-music, no ridiculously oversized breast enhancements, etc. Sometimes the scenerios may be a bit fantastic, but it rarely detracts from the enjoyment of the film.
It's been said that since you have the mosaic blocking the action, they can actually "fake" having sex. While this has happened with many actresses to varying degrees, lately it seems to happen less often as the girls are more open in nature.