Bitcoin is Cryptocurrency. Instead of using a printed currency, this can be used in digital form. Not controlled by any government or central banks, these currencies are validated by the miners, who get some bitcoin for their effort. The underlying technology behind Bitcoin is called Blockchain. Blockchain is nothing but a distributed ledger. That means, the ledger will be available in multiple computers (in fact millions of computers), so its records are immutable. In that way, hacking will be prevented. The idea of Bitcoin is avoid double spending and eliminate the money-sucking banks to act as middleman.