An Orc is a race alike goblins, but taller, and much stronger. These creatures are currently in the Hack/Mine mod, and they currently have one form.
These creatures once roamed the earth in great hordes, but after the great wars started by the Halflings these savage warriors have been reduced to smaller tribes scattered across the landscape. Only the bow users survived, but they're common wherever they appear.
There are only Orc Archers in the mod -- during the great wars, all the sword and axe users were killed. It's known that a lot of them just walked up to creepers and died, not knowing that you have to sprint at them to knock them back. They suffered the very most casualties during these wars, but there are still places where you can see lots and lots of orcs -- they are just rare and harder to find.