The Delta Quadrant was the region of space where the Borg originated. After the Cybermen turned against the Borg in their previously joint-invasion of Cogen V, the Cyber-Fleet headed for the Delta Quadrant, on a course for Borg space. (COMIC: Assimilation²)
Behind the scenes
In the Star Trek universe, our galaxy is divided into four quadrants. Earth is located in the Alpha Quadrant, with the United Federation of Planets having territory in both the Alpha and Beta Quadrants. There is also the Gamma Quadrant, primarily featured in Star Trek: Deep Space Nine. The Delta Quadrant is primarily featured in the spin-off series Star Trek: Voyager, where the titular starship travels through the quadrant throughout the show's run in order to get back home.