When you hear about blockchain, the word “decentralized” is used over and over again ad nauseam, to the point where the two terms seem synonymous. We describe blockchain as “decentralized” because there’s no single person or entity that verifies transactions on a blockchain. Rather, a network of computers does this. Together, these multiple computers discern whether a transaction in a blockchain network is accurate, and if they agree, that transaction becomes part of a new block on the chain.
This isn’t an inherently decentralized system, though. If a person or group of people can gain control of a majority of the computing power in a blockchain network, it can operate in a more centralized manner and the controllers of that majority can manipulate what gets recorded on the chain, accurate or not. A majority constitutes at minimum about 51 percent. Hence the name of one of blockchain’s biggest threats—the 51 percent attack.