In the context of blockchain and cryptocurrencies, a node refers to each computer running the Bitcoin client. So the Bitcoin network is made up of thousands of computer nodes spread around the world, and this is what makes Bitcoin a peer-to-peer, distributed economic system.
Each blockchain node is a communication point in the network. There are distinct types of nodes, and each type is responsible for performing a different set of functions. Taking Bitcoin as an example, the network nodes may be divided into four major groups: full nodes, listening nodes (supernodes), miner’s nodes, and lightweight or SPV clients.
Full nodes are the ones that really support and secure the Bitcoin blockchain, and they are indispensable to the network. Full nodes (or fully validating nodes) are responsible for verifying transactions and blocks according to the rules of the Bitcoin protocol. And since the network is distributed, the rules are enforced by Bitcoin’s consensus algorithm.
The so-called listening nodes, or supernodes, are the full nodes that are made publicly visible and accessible. As such, they can communicate with any other node that establishes a connection with them. So any fully validating node that is not hidden can be considered a listening node. This type of node is responsible for providing blockchain data to other nodes, but they may also function as a communication bridge.
The mining nodes are the ones that run specialized mining software, along with ASIC machines (in most cases). They invest a lot of resources hoping to get Bitcoin’s block reward. While solo miners are fully validating nodes, pool miners often provide computational resources without downloading the entire blockchain data. So only the administrator of the pool is required to run a full node.
Lastly, the lightweight or SPV clients are the ones that use the Bitcoin blockchain but don’t function as validating nodes. They simply gather information from supernodes, acting as a communication endpoint. As such, these nodes don’t keep a copy of the blockchain and don’t contribute to the security of the network.