Pornography is the graphic depiction of individuals engaged in sexual acts. Sex acts are varied but we usually are correct in assuming at least one partner is usually depicted as experiencing sexual pleasure, or penetration via a natural orifice.The genders and even species of the participants are not explicitly defined but the scene usually involves at least one human. All participants do not need to be biological entities (Given the human requirement, for example, his/her partner can simply be a robotic mechanism). Sex depicting non-human participants is not considered pornography (Farm animals procreating for example, but perhaps in certain contexts can be considered erotica -- Watching farm animals procreate on the farm -- not erotica, watching the film of the same act in an art museum maybe erotica given subjective proclivities, whether those stem from the viewer and/or the artistic author).
Pornography can be divided into Soft Porn and Hard Porn. Given Soft Porn, sexual partners are shown having sex but genital contact and penetration is implied and not actually shown. If erotica is used to describe soft porn it is certainly at the more extreme end of the spectrum. Hard porn involves the graphic depiction of sexual acts (despite Clintonian definitions) including oral manipulations of genitalia -- at least. One could say that if after watching hard porn he/she is merely titillated then that person was not paying attention, or so I'm told