Porno- is the Greek root for
whore,
prostitute; and pornocracy is one of those words you stumble across in a dictionary and wonder whether there could ever been a period in any country's history when it was ruled by whores. (That is, real whores, not common or garden politicians.)
It was not just any country, but the Papacy, at a particularly low point in its history. Sergius III got himself elected Pope by one faction in Rome in 898 but a rival faction prevailed and John IX got in. John lasted till 900, Benedict IV lasted till 903, and two rival popes Leo V and Christopher emerged then. This was Sergius III's big chance, and he deposed both of them and had them strangled. No, we haven't come to the low point yet.
Pope Sergius III lived until 911. One of his leading supporters Theophylact had a 15-year-old daughter Marozia, who was Sergius's lover. Their son in later years became Pope John XI, reigned 931-936. Actually all this was pretty much standard fare for the Popes of those days. Mistresses and nepotism were nothing.
The bit that galled church historians and made them dub this and the following decades the pornocracy was not that, nor that Theophylact was effective civil ruler of Rome, but that his wife Theodora and daughter Marozia were said to use sex freely to wield power.
Personally I think the hypocrisy is the low point. Or another candidate is the Cadaver Synod, just before, in 897, when Stephen VI accused his predecessor but one, Pope Formosus, of crimes against church law and put him on trial. This involved digging up the corpse and putting it in the dock, finding it guilty, dragging it through the streets, and flinging it in the Tiber. Anyway, Stephen lasted one year and was then strangled. They got through another two popes that year.