A node is a fundamental component in computer networks and blockchain systems. It refers to any device or point that can send, receive, or process data within a network. In blockchain technology, a node stores a copy of the distributed ledger and helps validate transactions, ensuring transparency and security. Nodes communicate with each other to maintain network consensus and prevent fraud. They can be full nodes, which store complete data, or light nodes, which store partial information. Overall, nodes play a vital role in maintaining decentralization, reliability, and efficiency across modern digital networks.