Ero-Guro, most frequently shortened to just 'Guro' is short for 'Erotic Grotesque'. It is a sub-genre of hentai
featuring blood, gore, disfiguration, torture, and bloody amputees. Many, if not most people to see it either see it funny, cool, or gross, although there are some that see it sexually attractive. Guro is just art, not real.
Guro is probably one of the least popular forms of hentai.