Distributed Ledger Technologies (DLTs)

A public ledger is a ledger that anyone can read. A distributed public ledger is a ledger that anyone is allowed to have a complete copy of, or perhaps even just the parts that they need. LDAP, replicating databases, DNS and blockchains are examples of distributed ledger technologies.

The primary difficulty in such systems is coming to agreement among all users of the ledger about what should be written in it and who is allowed to update it. The mechanism chosen for coming to such a common agreement is called the "consensus mechanism" of the ledger.