Most half-orcs result from orc chieftains capturing non-orcish women as wives. Orc-human and orc-goblin crosses are the most common, though sometimes a hobgoblin male in Chulan Toz will take an orcish concubine. Non-orcish women are considered to be at the bottom of the female hierarchy among orcish women, and their offspring have a similarly low status. Grown half-orcs are treated as regular orcs, but have to fight for any respect. (But so do most orcs.)
Sometimes a human male marries an orc female who has left orc society. The offspring of these matings are generally raised as humans, but may face discrimination as "monsters" in human society.
See the orcs culture page for more about orcs.