The word "orc" is actually an Old English word, used in Beowulf. Tolkien brought the word back into the English language as the name of the evil race of Orcs. In Tolkien's own books, Orcs is the same race as goblins. Since Tolkien did not invent the word (although he did invent the race) many other fantasy and RPG authors have used the name without running the risk of violating copyright.