A distributed 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 centralized data storage. - wikipedia
Distributed ledgers may be permissioned or permissionless regarding if anyone or only approved people can run a node to validate transactions. - wikipedia
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).
# See also