The Glessene sector was a region of space.
Deep Space 9's navigational computer held maps for this sector. In 2369, on stardate 46423, Kira Nerys tried to access maps of the Argosian sector but due to technical malfunctions, maps for the Glessene sector were retrieved instead. (DS9: "Babel")
This sector was only mentioned in dialogue.
According to StarTrek.com, this sector derived its name from the star Glessine and its star system. [1]