A pariah, outcast, or outsider was a person who was rejected by others as being hated, ignored or shunned.
In 2259, Lt. Commander Una Chin-Riley described the Illyrians as outcasts in her log, because their embracing of genetic modification was rejected by the United Federation of Planets. (SNW: "Ghosts of Illyria")
The Vendorian culture places considerable importance on the value of each individual. Those who were non-producers were considered useless, and deemed outcasts, fit only to do those tasks of the lowest order, such as being assigned to care for the injured and nurse them back to health. (TAS: "The Survivor")
In 2372, Rom was at Quark's Bar, Grill, Gaming House and Holosuite Arcade asking how Quark was, to which his answer was that he was broke, ruined, destitute, and a pariah. (DS9: "Body Parts")