A distributed ledger (also called a shared ledger, or distributed ledger technology, DLT) is a consensus of replicated, shared, and synchronized digital data geographically spread across multiple sites, countries, or institutions. There is no central administrator or centralized data storage.
A peer-to-peer network is required as well as consensus algorithms to ensure replication across nodes is undertaken. One form of distributed ledger design is the blockchain system, which can be either public or private.
The meaning of the word "blockchain" remains controversial. While some people[who?] state it is synonymous with a distributed ledger (and most of generalist press tends to use it with this meaning), others[who?] argue that technically it would only apply to linear blockchains such as the one Bitcoin or Litecoin use and not to directed acyclic graphs such as the ledgers based on Iota, Tangle, or Hedera Hashgraph algorithms. Therefore according to the latter definition, not all distributed ledgers have to necessarily employ a chain of blocks to successfully provide secure and valid achievement of distributed consensus: a blockchain is only one type of data structure considered to be a distributed ledger.[disputed ]
Distributed ledgers are mostly known because of their use as cryptocurrencies, even if technically speaking the cryptocurrency and the underlying ledger are two different things. However, in practice, a distributed ledger needs to have a cryptocurrency (proprietary or used from another ledger) in order to provide incentives to keep the nodes up and running.
Other possible uses beside cryptocurrencies include smart contracts (First introduced by Ethereum) or file storage.
In 2016, numerous banks tested distributed ledgers for international payments.
Incumbent banks are investing heavily in distributed ledgers as a cost-saving measure and a way to reduce operational risks. The future use of distributed ledgers is expected to monetize the Internet of things in a programmable economy.
Distributed ledgers may be permissioned or permissionless regarding if anyone or only approved people can run a node to validate transactions.  They also vary between the consensus algorithm. (Proof of Work, Proof of Stake, or Voting systems). They may also be mineable (you can claim ownership of new coins contributing with a node) or not mineable (the creator of the cryptocurrency owns all at the beginning).
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- Distributed Ledger Technology (DLT) and blockchain (PDF) (Report). World Bank. 1 December 2017. Retrieved 17 February 2018.
- "Central banks look to the future of money with blockchain technology trial". Australian Financial Review. Fairfax Media Publications. 21 November 2016. Retrieved 7 December 2016.
- "The CIO's Guide to Blockchain". Smarter with Gartner. Gartner. 29 June 2016. Retrieved 4 December 2016.