What is a blockchain?

A blockchain is defined as a decentralized, distributed ledger technology that records transactions securely and immutably across many computers. This key characteristic of decentralization means that no single entity has control over the entire network, which enhances security and trust. Each transaction is bundled into a block, and these blocks are linked together in chronological order, forming a chain—hence the name "blockchain." This structure ensures that once a transaction is recorded, it cannot be altered or deleted without the consensus of the network participants, which is referred to as immutability.

Moreover, the distributed nature of blockchain technology means that copies of the ledger are maintained on multiple nodes, providing redundancy and resilience against failures or attacks. This is in stark contrast to centralized systems, where a single point of failure can compromise the entire database. The use of cryptographic techniques in blockchains also secures the data, ensuring that only authorized parties can access or modify the information.

In summary, the description of a blockchain as a decentralized, distributed ledger technology captures the essential features that differentiate it from traditional databases and other technologies listed in the other choices.