Nodes are devices or data points on a larger network, in the context of crypto, they validate and relay transactions.
In a blockchain network, a node is a device that maintains a copy of the entire blockchain and helps to uphold the network's integrity by participating in the validation and relaying of transactions. There are different types of nodes, such as full nodes that store the complete blockchain history, and lightweight or SPV (Simple Payment Verification) nodes that store only a subset of the blockchain. Full nodes can independently verify every transaction without needing to trust other nodes, thus strengthening the security and decentralization of the network.
In the Bitcoin network, a full node would have a copy of the entire Bitcoin blockchain and can independently validate every transaction ever made on Bitcoin. Such a node helps to keep the network decentralized and resistant to censorship or manipulation.