Which of the following best describes a "peer" in a blockchain network?

In the context of a blockchain network, a "peer" is best described as a node that maintains a copy of the blockchain. Peers are integral components of the network, as they not only store the complete ledger of transactions but also participate in the process of validating and propagating new transactions and blocks. This decentralized nature ensures that the data remains distributed across many nodes, enhancing security and resilience against failures or attacks.

While it’s true that peers can play various roles, such as validating transactions or blocks, the fundamental characteristic is their role in maintaining the integrity and availability of the blockchain by having their own copy of it. Peers communicate with one another to ensure that all copies of the blockchain remain consistent, contributing to the overall consensus mechanism of the network.

The other choices do not capture the essence of what a peer is in a blockchain context. For instance, a user who can only view data does not have the active role or the responsibilities that a peer holds. A central server contradicts the decentralized structure of blockchain, and while entities responsible for transaction approval might exist, they typically refer to the collective agreement mechanism of the network rather than an individual peer itself.