The Abyss nebula is a large gas cloud on the outer edge of the galaxy, in the Beta Quadrant.
It was first surveyed in 2234 by the USS Byrd, and is composed primarily of interstellar dust. It is registered as "Stellar Catalog Beta 14-CN 625." It is standard information in the library computer of starships in the late 23rd century.
One particular region of the nebula is known as "Alpha CN625." (Game: "STA: SC")