A known personality who is only or mostly famous for their work on reality TV, getting pics taken by the paparazzi, putting out sex tapes and/or going on multiple talk shows. Someone who is famous and/or talked about without actually having any talent or actual career other than being and promoting themselves. A person who is famous only for being well known.
Paris Hilton is a prime example of being a pseudoceleb. The housewives on Bravo are pseudocelebs. Snooki and the Jersey Shore cast are all pseudocelebs. Scott Disick is a hanger on Kardashian and lives off being a pseudoceleb by hosting parties at nightclubs. Many has been famous people drift into being pseudocelebs when they get desperate for attention and/or money.