Orcs are a common Dungeons and Dragons race, drawn in the Order of the Stick with light green skin and roughly the same size as humans. They are stupid and sometimes childlike and have bold speech balloons, always speaking in third person and without capital letters. Many orcs, including Chief Grukgruk and Shaman Vurkle inhabited an island that was explored by Elan, Durkon, Daigo and Lien. A tribe of orcs also appeared in the prequel book On the Origin of PCs, who were camping by a town to get backstage tickets to a rock concert.
Half-orcs are the result of orcs breeding with humans. We have seen three so far in the comic: Thog, Therkla and Bozzok. Thog is very orc-like in the way he acts, while Bozzok and Therkla seem to behave more like humans.