Because monstrous humanoids like orcs are evil spirits made flesh, they don't reproduce as regular mortals do. There can't be the offspring of orcs and humans.

The race represented in the Player's Handbook are the lowest caste of elves in the Conclave. They are called Green Elves, and are sometimes pejoratively called half-orcs. They use the Player's Handbook statistics of half-orcs to represent them. They have lifespans similar to that of humans and must sleep to rest.