Bitcoin is an open-source cryptocurrency protocol and direct payment network which utilizes peer-to-peer technology for operations with no central authority or banks.
A "bitcoin" (lowercase) is the currency used by Bitcoin protocol. It is usually abbreviated as "BTC."
Transaction management and the issuing of new "bitcoins" is carried out collectively by a network of nodes. Although other cryptocurrencies have existed before Bitcoin, Bitcoin is the first decentralized cryptocurrency which solved the "double spending" problem, using a distributed blockchain.
The first Bitcoin specification was published in 2009 in a cryptography mailing list by Satoshi Nakamoto (read the original Nakamoto's paper). After that, Nakamoto developed and published the first Bitcoin reference software client as an open source project (code hosted in a GitHub repository).
Bitcoin provides the means for direct payments between individuals without an intermediary, in contrast with the existing system where every payment is processed by an existing monetary authority such as a bank. Taking out of the picture a centralized authority creates one of the currency’s defining features: Decentralized currency transactions.
For the casual user, Bitcoin is just a software application (mobile or desktop) that provides a personal Bitcoin wallet and allows users to send and receive bitcoins.
With the most extensive variety of markets and the most prominent value and volume - having reached a peak of 81 billion USD - Bitcoin is considered the father of all cryptocurrencies. It is also the most traded cryptocurrency.
Bitcoin is considered nowadays as one of the leading entry points for all the other cryptocurrencies. The price is viewed by traditional traders quite volatile, and it can go up or down by 5%-10% in a single day.
Bitcoin's Proof Of Work (PoW) algorithm is SHA-256.
There is a fixed amount of coins to be generated by mining at 21,000,000 total minable coins.
The block generation time is currently at 10 minutes.