Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services, but the real-world value of the coins is extremely volatile. Research produced by the University of Cambridge estimated that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin .
Bitcoin has been criticized for its use in illegal transactions, the large amount of electricity (and thus carbon footprint) used by mining, price , and thefts from exchanges. Some economists and commentators have characterized it as a speculative bubble at various times. Bitcoin has also been used as an investment, although several regulatory agencies have issued investor alerts about bitcoin .
The word bitcoin was defined in a white paper published on 31 October 2008. It is a compound of the words bit and coin. No uniform convention for bitcoin capitalization exists; some sources use Bitcoin , capitalized, to refer to the technology and network and bitcoin , lowercase, for the unit of account. The Wall Street Journal, The Chronicle of Higher Education, and the Oxford English Dictionary advocate the use of lowercase bitcoin in all cases.