A blockchain node is a computer or software instance that participates in a particular blockchain network. Its tasks depend on the network and the type of node.
What nodes can do
Bitcoin full nodes download and verify blocks and transactions before relaying them to other nodes. Ethereum describes a node as an instance of Ethereum client software connected to other computers running Ethereum software.
These descriptions show why “node” is a broad term. A node can communicate data, check data against protocol rules, retain some data and support the network. It is not automatically the same thing as a validator or miner.
Different types of node
Nodes do not all retain the same amount of information. Bitcoin distinguishes archival and pruned full nodes. Ethereum documentation distinguishes light, full and archive nodes. The labels and technical details are specific to those networks.
Ethereum’s current architecture also separates execution-client and consensus-client software. A validator component is an additional, distinct role in that system.
What a node does not guarantee
Running or referring to a node does not establish that every historical record is stored locally, that someone is identified, or that an external claim is accurate. The answer depends on the software, configuration and network being discussed.
Sources
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