A recluse was an individual who lived apart from society by choice.
Prior to the USS Enterprise-D's visit to Kaelon II in 2367, Captain Jean-Luc Picard informed Ambassador Lwaxana Troi that their upcoming mission was "something of a rather delicate situation" on account of the fact that it was "the first real contact with a rather reclusive race," known as the Kaelon. (TNG: "Half a Life")
In a 2370 discussion between Beverly Crusher and Jean-Luc Picard about the inclusion of only half of a planet Kesprytt's people into the Federation, Crusher pointed out that the considered half, the Kes, were "a very unified, very progressive people." Picard, however, countered that "the Prytt are not. They are reclusive to the point of xenophobia." (TNG: "Attached")