The Argosian sector was a region of space.

Deep Space 9's navigational computer held star charts to this sector. However due to technical malfunctions, when Kira Nerys tried to access these, maps of the Glessene sector were retrieved instead. (DS9: "Babel")

This sector was only mentioned in dialogue.
The Star Trek Encyclopedia (4th ed., vol. 1, p. 44) located the Argosian sector in the Alpha Quadrant.