There are standard goblins as a race and using various classes as found in the core materials, but then are specific homebrew goblin subraces, social divisions, historical notes and whatnot in this game.
The Zerk Goblins were standard goblins who once inhabited the Zerk Swamp in the greater Goldvale area, long, long ago. At the same time they existed, so did the Toc Clan Dwarves, who counted as one of their enemies. For a long time these goblins did great in their swamp lands, until the infamous Alden came and converted them into a force for himself which led to the Toc Clan Coal Mine Event.
The Coal Goblins are the descendants of the Zerk Goblins, those left over after the Toc Clan Coal Mine Event. They take their name, or maybe they've been branded with it, from the coal mine that the event took place in, and took the Old Dwarven Keep above as their new home, never returning to the Zerk Swamp. Likely the most well known in our game is Leithe.