Bitcoin is a digital asset and a payment system invented by Satoshi Nakamoto. Transactions are verified by network nodes through cryptography and recorded in a public dispersed ledger called a blockchain.
Bitcoin is unique in that there are a finite number of them: 21 million.
Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services.
As of February 2015, over 100,000 merchants and vendors accepted bitcoin as payment.
Bitcoin has been criticized for its use in illegal transactions, its high electricity consumption, price volatility, and thefts from exchanges. Some economists, including several Nobel laureates, have characterized it as a speculative bubble.
Investing in Bitcoin is not for the faint of heart. Bitcoin is a highly volatile asset, and its value can move up or down drastically in short periods of time. It is important to understand the risks associated with investing in cryptocurrency before you begin, as it is not backed by any government or central bank and carries a unique set of risks. Make sure you do your research, understand the technology behind it, and never invest more than you can afford to lose.
Bitcoin has also been used as an investment, although several regulatory agencies have issued investor alerts about bitcoin.
The unit of account of the bitcoin system is a bitcoin. Ticker symbols used to represent bitcoin are BTC[b] and XBT.
[c] Its Unicode character is ₿.[d].
Small amounts of bitcoin used as alternative units are millibitcoin (mBTC), and satoshi (sat). Named in homage to bitcoin’s creator, a satoshi is the smallest amount within bitcoin representing 0.00000001 bitcoins, one hundred millionth of a bitcoin.
 A millibitcoin equals 0.001 bitcoins; one thousandth of abitcoin or 100,000 satoshis..