A distributed ledger (also called shared ledger) is a consensus of replicated, shared, and synchronized digital data geographically spread across multiple sites, countries, or institutions.
There is no central administrator or centralised data storage.
A peer-to-peer network is required as well as consensus algorithms to ensure replication across nodes is undertaken.
One distributed ledger design is through implementation of a public or private blockchain system. But all distributed ledgers do not 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.