Orc is the anglicised version of the Sindarin word yrch, the servants of the Ainur Melkor. They were most likely created by the perversion of Elves, Melkor being unable to create anything of his own. As such, they shared the immortality of the Elves, but not their appearance. Black, sallow, and stunted, most preferred darkness, however breeds such as the Uruk-Hai were able to endure sunlight.

Tolkien referred to the Orcs as Goblins in The Hobbit, but they're the same thing.