A node is a computer that maintains a copy of the blockchain and relays transactions to its peers. Nodes are the network. Without them, there is no blockchain, only a database on someone's server. A full node stores the entire chain and validates every transaction. A light node stores only headers. A mining node or validator node participates in consensus. An archive node keeps every historical state, which is useful for block explorers and analytics.

Running a node is how you verify the chain yourself. You do not trust an explorer to tell you your balance. You check it against the copy on your own hardware. That independence is the point. The more nodes there are, the harder it is for anyone to change the rules or censor transactions. Ethereum has thousands of nodes. Bitcoin has tens of thousands. Some chains have only a handful, which makes them vulnerable to capture. Node count is a rough measure of decentralization, though not a perfect one. What matters is who runs the nodes and whether they are independent.

Node types

• Full node — stores and validates the entire blockchain
• Light node — stores headers, relies on full nodes
• Mining node — full node that also produces blocks
• Archive node — keeps all historical state
• Validator node — proof-of-stake equivalent of a mining node

Running a node costs storage, bandwidth, and some technical effort. It is not for everyone. It is the strongest way to use a blockchain without trusting anyone else.