Pornography
Pornography is any picture or video using nudity or sexual acts to cause sexual desire? in the viewer. The word comes from two Greek words, porneía ("fornication, prostitution") and gráphō ("I depict").
Pornography should not exist. It's inappropriate to share sexual pictures of people. It ruins your sexual purity. Intimate photos might be fine between a husband and wife, though. Don't look at porn.
Pornography is not a documentary. A lot of people are getting their sex education (or miseducation) from pornography, but that is disastrous. Pornography is fiction, possibly the most fictional thing that exists. Listen to a website like this one instead.
In real life recording a man? and a woman having sex are usually real close to each other and there's not much the camera can see except for the people's sides and the man's bum. So myriads of variants of porn are filmed to keep it interesting—otherwise you'd get bored of porn quick.
All the porn of the past, from sketches to DVDs, is not the same as modern internet porn in intensity or addictiveness.