In Tolkien's mythology, wargs can be marked out from a normal wolf by their size and relative intelligence. They're capable of allying themselves to another species— usually Goblins— and can be ridden like horses. Wargs are also capable of carrying out purposeful attacks on their own, rather than just hunting for
In The Fellowship of the Ring, they did just this to the Fellowship outside of Moria after becoming agents of Mordor. We also saw wargs used by Azog and his Orc troops towards the climax of The Hobbit: An Unexpected Journey, nearly sending Gandalf and the rest of the company tumbling over a cliff as they took refuge up a tree, and almost knocking the life right out of Thorin.