Blockchain: The financial system to validate Bitcoin transactions is known as the Blockchain, and depends on a decentralised network of computers connected over the internet.
Like peer-to-peer (P2P) networks where unidentified people upload and download music and films, the blockchain depends on a growing community of people and institutions online.
Those peers run the Bitcoin software to verify Bitcoin transactions, independent of any bank or treasury.
Every time people exchange Bitcoins online, the whole network gets updated with the new information, creating new "blocks", i.e. long chains of data for computers to solve.
Mining farms: Like printing new bank notes, new Bitcoins are created by solving "blocks" of mathematical equations that are created each time Bitcoins are exchanged online.
Even though the Bitcoin software can crunch all those equations automatically, it requires a lot of computing power to do so.
This automatic process is known as "mining" and requires a lot of computing power. For this, large data centres, known as "mining farms", have been set up. Many of the largest farms are located in Russia and China.
Blockchain.info counts 16 million Bitcoins in circulation, while there can only be up to 21 million Bitcoins. This limit is set in the Bitcoin algorithm.