Star Trek: Deep Space Nine (or DS9) was the third live action Star Trek television series, which aired from January 1993 to May of 1999. During in and after the TV series it has spawned numerous other stories in prose, comics and other media.
Unlike the previous Star Trek, set on starships, Deep Space Nine's primary setting is a space station, Deep Space 9, formerly the Cardassian station Terok Nor. The station is a key strategic location, near to the planet Bajor, itself near the Cardassian border, and most significantly (following the events of the first episode) the station is situated next to the Bajoran wormhole, giving access to the Gamma Quadrant. The station also had a complement of runabouts, and later the USS Defiant, allowing stories to take the characters away from the station itself.
Due to the mostly stationary situation of the series, DS9 tended more toward continuing stories, rather than the "alien of the week" approach common to other series. Some of the main arc's involved: the Bajorans growing from years under occupation by the Cardassians, eventually joining the Federation; Captain Sisko's role as the Emissary; and the build up to, eventual breakout, and aftermath of, the Dominion War.