Sector 3556 was a region of space in the Delta Quadrant. This sector was located nearly two hundred light years from a point beyond the Denkiri Arm, a galactic arm located in the Gamma Quadrant.
In 2366, the terminus of the Barzan wormhole shifted from its location in the Gamma Quadrant to a new location in this sector. In that year, the Ferengi Arridor and Kol were stranded in Sector 3556 when they traveled through the wormhole but did not re-enter it before the terminus shifted again. (TNG: "The Price")