TL;DR: A blockchain node is a computer running software that maintains a copy of the blockchain, verifies transactions, and relays data across the network. Nodes are the backbone of every blockchain. Without them, there is no network. Different types of nodes serve different purposes, from lightweight nodes that verify transactions to full archive nodes that store the entire history of the chain.
The Simple Explanation
Every blockchain is a peer-to-peer network, which means there is no central server. Instead, thousands of individual computers (nodes) work together to keep the network running. Each node runs client software that connects it to other nodes, downloads a copy of the blockchain, validates new transactions and blocks according to the consensus rules, and shares data with the rest of the network.
When you send a transaction on Ethereum, Solana, or any other blockchain, your transaction does not go to a single company's server. It gets broadcast to the network and picked up by nodes. Those nodes check that the transaction is valid (correct signature, sufficient balance, proper formatting), include it in a block, and propagate the confirmed block across the network. Every node independently verifies every block, which is what makes blockchain trustless. You do not need to trust any single node because they all check each other's work.
Running a node is how you participate in the network at the most fundamental level. It is also how applications interact with the blockchain. When a wallet shows your balance, it is querying a node. When a dapp executes a smart contract, it is sending a transaction through a node. When an analytics platform tracks onchain activity, it is reading data from a node. Nodes are the gateway between your application and the blockchain
Types of Nodes
Not all nodes are created equal. The type of node you run (or connect to) depends on your use case, resources, and how much historical data you need access to.
