What is a Bitcoin node?

A Bitcoin node is essentially a computer running the Bitcoin software that participates in the Bitcoin network. Nodes perform various tasks crucial to the functioning of the network, including:

1. **Relaying transactions:** Nodes receive, verify, and broadcast transactions to other nodes in the network. This helps in propagating transactions across the network efficiently.

2. **Validating transactions and blocks:** Nodes check the validity of transactions and blocks according to the consensus rules of the Bitcoin protocol. They ensure that transactions adhere to the rules (e.g., no double-spending) and that blocks are created according to the protocol (e.g., correct proof-of-work).

3. **Maintaining a copy of the blockchain:** Nodes store a complete copy of the entire Bitcoin blockchain, which contains a record of all transactions ever made on the network. This allows them to independently verify the history of transactions and blocks.

4. **Participating in the consensus process:** Nodes contribute to the decentralized consensus mechanism of Bitcoin by accepting or rejecting new blocks proposed by miners. They follow the longest valid chain rule to determine the valid blockchain.

Nodes can be categorized into different types based on their role and level of participation in the network. Full nodes maintain a complete copy of the blockchain and participate in all aspects of the Bitcoin network, while lightweight nodes (such as SPV nodes) perform fewer tasks and rely on full nodes for certain operations. Having a diverse network of nodes helps ensure the decentralization and security of the Bitcoin network.