Sector 864

Sector 864 was a region of space in the Alpha Quadrant. This sector was in Cardassian space. The uninhabited planet Celtris III was located in this sector.

In 2369, after the capture of Captain Jean-Luc Picard in the caverns of Celtris III by Cardassian soldiers, the USS Enterprise-D detected many coded messages coming from this planet. (TNG: "Chain Of Command, Part I")

This sector's quadrant of origin is inferred based on the position of the Cardassian Union in the star chart appearing in the Star Trek: Picard episode "Maps and Legends".
This sector was named in an Okudagram seen at Science 1 on the Enterprise bridge. This graphic was later put up for auction in 2018. [1]