Orcs are not just something from Tolkien. In the Silmarilion, we learn that orcs are created from tortured and corrupted elves.

In D&D orcs have an influence from Tolkien, but the word is from Orcus, for an ancient diety of the underworld. It is also connected to ogre. In D&D, Orcus is used as the name of the ruler of the undead, skeletons, zombies, wights, vampires, etc.

In the Monster Manual, the classic illustration are of creatures that appear to have the head of a pig.

If you have ever seen Return of the Jedi, the Gamorrean Guards reminded me of the D&D orcs. Players from my era think of D&D orcs when they see the Gamorrean Guards. Too funny.