Orcs (also known as "Orsimer") are a race of hardy green-skinned elves hailing from the Wrothgarian mountain. Orcs are generally reviled by people from other races. They are reputed as skilled blacksmiths and warriors. Being an Orc gives you a +5% bonus to your Armor Rating and a +5% bonus to the damage you deal with Abilities.
For more information, see the main lore article.