What is Hentai?

Hentai:

A relatively large proportion, compared with western comics, is porn. Often these 'normal' in the stores and some local convenience stores or konbini 'available, Japanese hardly take offense and see it more as fantasy. This type of manga is called Hentai in Europe.

One of the most known/poplair Hentai sites is Rule34.
Check it out if you want :p

ps: RULE34 IS BEST!