Ero guro nansensu, frequently shortened to ero guro is a wasei-eigo term that describes a literary and artistic movement originated in 1920-1930 in Japan. Ero guro puts its focus on eroticism, sexual corruption and decadence. While ero guro is a specific movement, many of its components can be found throughout Japanese history and culture.
In actuality the "grotesque" term implies malformed, unnatural or horrific. Items that are pornographic and bloody are not necessarily ero guro, and ero-guro is not necessarily pornographic or bloody. However, the term is often used incorrectly by western audiences to mean "gore" - depictions of horror, blood, and guts.