A hedge is a living fence made of closely planted bushes, which, as they grow and get trimmed and shaped, form a wall of green.
Hedge can also be used as a verb. If someone asks you a question and you hedge, you're avoiding a straight answer. If you're not sure what your boss's political views are, you can hedge by not revealing yours. If you hedge your bets, you're trying to minimize risk or loss — that is, you're trying to cover yourself no matter what happens.