Bitcoin is the first digital currency whose white paper was published in 2009 by the pseudonym Satoshi Nakamoto. Since the amount of all bitcoins is limited to 21 million, only supply and demand determine the price of a bitcoin.
Bitcoin is based on blockchain technology, which means it is independent of all central banks. All transactions are anonymous but visible to every participant.
Bitcoin can be bought, sold, or even mined yourself. In this case one speaks of mining.