Refers to a public ledger, or database, that in theory cannot be changed without consensus. This immutability allows for data within that database to perform different transactional functions, and the elements of this database are known as blocks. These blocks can represent movements of value, like a currency, or work as an access mechanism or functional utility, for a platform providing goods and services. As more transactions take place on a ledger, new blocks are added to the chain containing the recorded transaction data. There are different ways of generating and managing blockchains. Some are mined, others are pre-minied. Each has a different amount of data it can store, and there are large variations of speed in which the data can be transferred. Some blockchains are managed centrally by specialized parties that run nodes in the network, and might more accurately be termed distributed ledger technology, and others like the Bitcoin blockchain are completely decentralized. There also exists hybrid systems, which aim to combine the benefits of centralisation and decentralisation.