Bitcoin is the first and most widely recognized cryptocurrency. It enables peer-to-peer exchange of value in the digital realm through the use of a decentralized protocol, cryptography, and a mechanism to achieve global consensus on the state of a periodically updated public transaction ledger called a 'blockchain.'
Practically speaking, Bitcoin is a form of digital money that (1) exists independently of any government, state, or financial institution, (2) can be transferred globally without the need for a centralized intermediary, and (3) has a known monetary policy that arguably cannot be altered.
Bitcoin can refer to the Bitcoin software protocol as well as to the monetary unit, which goes by the ticker symbol BTC.
Launched anonymously in January 2009 to a niche group of technologists, Bitcoin is now a globally traded financial asset with daily settled volume measured in the tens of billions of dollars. Although its regulatory status varies by region and continues to evolve, Bitcoin is most commonly regulated as either a currency or a commodity, and is legal to use (with varying levels of restrictions) in all major economies.
Bitcoin is based on the ideas laid out in a 2008 whitepaper titled Bitcoin: A Peer-to-Peer Electronic Cash System.
The paper detailed methods for "allowing any two willing parties to transact directly with each other without the need for a trusted third party." The technologies deployed solved the 'double spend' problem, enabling scarcity in the digital environment for the first time.
The listed author of the paper is Satoshi Nakamoto, a presumed pseudonym for a person or group who's true identity remains a mystery. Nakamoto released the first open-source Bitcoin software client on January 9th, 2009, and anyone who installed the client could begin using Bitcoin.
Initial growth of the Bitcoin network was driven primarily by its utility as a novel method for transacting value in the digital world. Early proponents were, by and large, 'cypherpunks' - individuals who advocated the use of strong cryptography and privacy-enhancing technologies as a route to social and political change. However, speculation as to the future value of Bitcoin soon became a significant driver of adoption.
The price of bitcoin and the number of Bitcoin users rose in waves over the following decade. As regulators in major economies provided clarity on the legality of Bitcoin and other cryptocurrencies, a large number of Bitcoin exchanges established banking connections, making it easy to convert local currency to and from bitcoin. Other businesses established robust custodial services, making it easier for institutional investors to gain exposure to the asset as a growing number of high-profile investors signaled their interest.
At its most basic level, Bitcoin is useful for transacting value outside of the traditional financial system. People use Bitcoin to, for example, make international payments that are settled faster, more securely, and at lower transactional fees than through legacy settlement methods such as the SWIFT or ACH networks.
In the early years, when network adoption was sparse, Bitcoin could be used to settle even small-value transactions, and do so competitively with payment networks like Visa and Mastercard (which, in fact, settle transactions long after point of sale). However, as Bitcoin became more widely used, scaling issues made it less competitive as a medium of exchange for small-value items. In short, it became prohibitively expensive to settle small-value transactions due to limited throughput on the ledger and the lack of availabily of second-layer solutions. This supported the narrative that Bitcoin's primary value is less as a payment network and more as alternative to gold, or 'digital gold.' Here, the argument is that Bitcoin derives value from a combination of the technological breakthroughs it integrates, its capped supply with 'built-into-the-code' monetary policy, and its powerful network effects. In this regard, the investment thesis is that Bitcoin could replace gold and potentially become a form of 'pristine collateral' for the global economy.
Another popular narrative is that Bitcoin supports economic freedom. It is said to do this by providing, on an opt-in basis, an alternative form of money that integrates strong protection against (1) monetary confiscation, (2) censorship, and (3) devaluation through uncapped inflation. Note that this narrative is not mutually exclusive from the 'digital gold' narrative.
Read more: How does governance work in Bitcoin?
Read more: What is Bitcoin mining?
Bitcoin is not a static protocol. It can and has integrated changes throughout its lifetime, and it will continue to evolve. While there are a number of formalized procedures for upgrading Bitcoin (see "How does Bitcoin governance work?"), governance of the protocol is ultimately based on deliberation, persuasion, and volition. In other words, people decide what Bitcoin is.
In several instances, there have been significant disagreements amongst the community as to the direction that Bitcoin should take. When such disagreements cannot be resolved through deliberation and persuasion, a portion of users may - of their own volition - choose to acknowledge a different version of Bitcoin.
The alternative version of Bitcoin with the greatest number of adherents has come to be known as Bitcoin Cash (BCH). It arose out of a proposal aiming to solve the above-described problems scaling problems that resulted in rising transaction costs and increasing transaction confirmation times. This version of Bitcoin began on August 1st, 2017.