A computer on the Internet that has a complete or abbreviated copy of the Bitcoin blockchain. There are full nodes, lightweight nodes and mining nodes, the latter adding transactions to blocks on the blockchain (see Bitcoin mining
Full Nodes vs. Lightweight SPV Nodes
Full nodes maintain a complete copy of the Bitcoin blockchain. Full nodes may include a wallet for coin storage, support Bitcoin network routing and transaction validation. For example, an organization that accepts Bitcoins may want to validate transactions more quickly and not wait for the miner to place them on the blockchain. Miners are also full nodes.
Full nodes ensure that transactions and blocks conform to consensus rules, which mean that they must be correctly formatted and that people cannot spend their coins more than once (double spend). They can also detect fraud if the mining reward for the block is not correct.
Although some Bitcoin professionals believe non-mining full nodes strengthen the network, opponents claim they just get in the way and slow everything down.
Simplified payment verification (SPV) nodes only store the headers and not the entire blockchain. SPVs can perform wallet and routing functions, and they can check if a transaction is included in the blockchain. They can also interact with full nodes to determine if a transaction has been validated, and they can be notified by full nodes that a transaction affects them. See Bitcoin mining