Bitcoin is a worldwide cryptocurrency and digital payment system, called the first decentralized digital currency, as the system works without a central repository or single administrator. According to great wiki. Decentralized has also downside w/c leads to some splits. But decentralization is also good with the premise of no single entity, government or institution that would dictate bitcoin. It should be the community. But with the rise of large miners seems the process are going centralized again because the primary goals should be the process are distributed to different nodes and to avoid a single node to have a majority of the transactions.