A node, in simple terms, is any device that participates in a blockchain network.
Normally, nodes are computers or servers that provide some function to the network they’re connected to.
A node’s role is dictated by the protocol of the network.
Nodes can have different duties within a network, but most nodes are tasked with keeping track of and verifying network transactions.
Some nodes also act as communication hubs on the network, relaying and routing network requests and data to other nodes, miners, and validators.
Nodes and miners form the backbone of the Bitcoin network and other blockchain networks.
Anyone can become a node operator or miner without permission from some central authority.
As long as you can connect to the Internet, you can run a node or miner from anywhere in the world.
This is what makes a blockchain network, like the Bitcoin network, decentralized and almost impossible to shut down.