these analogies are terrible because they are apples and oranges half the time. It's like X was to Y doesn't solve anything.
Bitcoin is an anonymous, decentralized, unregulated digital currency and is protected from duplication by proof of it's existence from communal "work" or calculations similar to password cracking (or very simply, complex math that only computers are equipped for); the value is determined entirely by the holders of the coins.
I can't imagine a way to simplify it better than that.