"Gold is money and all the rest is credit" -JP Morgan

Money is a commodity of inherent value, in particular gold, which is the most durable commodity and therefore the best form of physical savings and has therefore been chosen by the market as money.

Credit is a promise to pay money.

Currency is a credit instrument which promises to pay the bearer some amount of money on demand. The current "pound sterling" notes still print this false promise on their face. US law still guarantees that Federal Reserve Notes shall be redeemed on demand. Of course, neither promise is honored.

Bitcoin is a (crypto) currency, a digital currency cryptographically secured. It is not a commodity because there are no Bitcoins. Instead it is a ledger entry that cannot be redeemed, just like fiat bank deposits or fiat notes.