Star Trek: Deep Space Nine (sometimes abbreviated to DS9) is a science fiction television series set in the Star Trek universe in the Milky Way galaxy, in the years 2369–2375. In contrast to other Star Trek TV series, it primarily takes place on a space station rather than a starship, so as not to have two series with starships in the same time period; the series ran concurrently with Star Trek: The Next Generation during its first two seasons and with Star Trek: Voyager for the remainder of its run. The starship USS Defiant was introduced in season 3, but the space station Deep Space Nine remained the series' primary setting.

References:
https://en.wikipedia.org/wiki/Star_Trek:_Deep_Space_Nine