Node
Plain English
A computer that participates in the blockchain network by storing a copy of all transactions and helping verify new ones. Like having a full copy of the blockchain ledger on your computer. More nodes = more decentralized and secure the network is.
Technical
An individual computer running blockchain client software that maintains a copy of the distributed ledger and participates in consensus. Full nodes store complete blockchain history and validate all transactions. Light nodes store minimal data and rely on full nodes. Validator nodes actively participate in block production and consensus.