A decentralized ledger in blockchain is a type of distributed database technology that allows multiple parties to maintain a shared, secure, and tamper-proof record of transactions without the need for a central authority.

In a decentralized ledger blockchain, each node on the network maintains a copy of the ledger, which contains a record of all the transactions that have taken place. Transactions are grouped together into blocks, which are then added to the chain of blocks (hence the name blockchain) in a linear, chronological order. Each block contains a reference to the previous block in the chain, creating an immutable record of all the transactions that have ever occurred on the network.

Because the ledger is maintained by a distributed network of nodes, it is much more secure and resilient to attacks than a centralized database. In order to alter the ledger, an attacker would need to compromise a majority of the nodes on the network, which is a difficult and resource-intensive task.

Decentralized ledger blockchains are used in a variety of applications, including cryptocurrencies, supply chain management, voting systems, and identity management, among others. By providing a secure, transparent, and decentralized platform for recording transactions, blockchain technology has the potential to revolutionize many industries and reshape the way we think about trust and accountability in the digital age.