Node

A node is any computer that participates in a blockchain network by running its software. Full nodes download and verify every block and transaction against the protocol rules, keeping an independent copy of the entire history. They reject anything invalid regardless of who sent it, which is how the rules are enforced without a central authority.

Not all nodes produce blocks. On Bitcoin, miners are nodes that also do the proof-of-work search, but tens of thousands of non-mining full nodes simply validate and relay. On Ethereum, validators are nodes that have staked ETH and participate in consensus, while many other nodes just serve data. Light nodes store only block headers and rely on full nodes for details.

Running a node is the most direct way to use a blockchain without trusting a third party. A Bitcoin full node needs several hundred gigabytes of storage and a home internet connection. Ethereum nodes need more. Wallets that connect to your own node confirm balances independently rather than asking a company's servers.