Classic definition is: written or visual material designed to appeal to prurient interest or invoke sexual reaction. Word has built in bad connotation.
In reality pornography extends far beyond this, to include any image or text that can possibly appeal to anyone with even the wildest, sickest fetish or interest, or even a fetish that, on the surface can be seen as mundane.
Did you see those pictures of baby seals getting clubbed to death? That was really pornography.Women being raped and left with rubber masks on their face is reallypornography.There was a fire at the old warehouse last night. I watched it and masterbated at the same time. It was really pornography. Those pictures of genocide and babies dying of hunger in Africa were really pornography.