Japanese for "pervert." Literally "strange desires." In American usage it more often refers to Japanese porn, especially in cartoons.
(The plural of "hentai" is just "hentai," not "hentais.")

if youve ever seen hentai then you will be put into one of 3 groups
1)lovers
2)loathers
3)laughers

1)lovers are the ones who basically love hentai, i dont think their is anything wrong with it, as long as they dont take it waaaaay too seriously

2)loathers, lovers worst nightmare, go round saying nerds jack off over this and that real women are better, this may be obviously true but i dont criticise peoples beliefs

3)ah, my group. laughers are the guys who see it and just start laughing at it, not hating it, but not loving it either, these are the guys who play games like franks adventure and those damn simgirl games just forthe hell of completing it before their friend (who happens to be a lover)

overall there is nothing wrong with it, as long as they keep it clean, when they show little children and women getting done by slimy tenticles, thats VERY wrong! love it or loathe it though, its here to stay.

mostly what everyone else said. all i want is for someone to post an image. ^__^

The honed science of painstakingly designing young Japanese girls with the greatest rapability ever imagined.

The difference between Hentai and Anime is simply this. Hentai is art of a Japanese drawing style that depicts sexually explicit scenes.

Anime is art of a Japanese drawing style not depicting sexually explicit scenes, though usually tells a story of fantasy or something that can't be done in real life.

Hentai is a particular type of anime which is specifically about sex in any way, shape, or form. It may manifest itself in still picture, movie, or video game form. Most commonly it is just typical porn, but with anime characters. However, because it is animated, it sometimes can be even more sick, depraved, and downright revolting than any live action porn has ever been or ever will be. For example: One hentai movie may feature a man having sex with one or more women. That's just your basic porn. But some of the sickest hentai will tend to involve one or more of the following: Rape, Bestiality (sex with animals), Children (pedophelia), Tentacles (yes, like on an octopus), or pretty much anything sick you can think of. Depending on where you get your hentai, it can be perfectly acceptable porn, or a disgusting blemish on the face of humanity's creative tendencies. So beware. Tends to feature better-than-average-looking women with breasts that defy the laws of physics, strangely colored hair and, sometimes, unexplained animal ears. (These last two tend to crop up in all anime.)

the best thing in the world

Drawn porn. They've got all kinds of weird shit happening in and out. Tentacles, aliens, incest etc. In Japan, it simply means "pervert" (well, from what I've been told and read).

Really decent (save for yeah, those other weird types that utterly destroy your sanity if watched for long) as long as you don't start dreaming of those drawn girls, or you'll be digging your own grave.

It's interesting and in a way stimulating. I repeat again: As long as you realize that some weird shit there won't come true, the girls are JUST drawn, the body figures are out of rational proportion and not live in that "drawn" world it's all fine.

There are also dating sims out there and like previously mentioned, are sim-girl -related (Guy meets a lot of girls and screws them all then weird shit happens at the end). However, some do have stories. These games focus more on how to attain the girl in a focused manner without getting too much sex in between (I mean only at the end or if your "chosen path" is the girl you are pursuing; Even at the middle, you'll get laid. Easy shit, CAN be possible, but mostly impossible unless.. I don't know). Not only these sim-girled games focus on one girl, but focus on the whole story in general. All games (H-games) have different genres. Worth your time if you really don't have anything to do, or just want something else to meddle with.

All in all, hentai's good to a degree. Great alternative for real porn. Just realize none of those shit will happen in real life.

Hentai is essentially animated pornography that often involves monsters and many, many penis tipped tentacles that magically extend from just about anything the animators want it to. Shoving random materials into various orrifices is also quite frequently seen.