A node is a fundamental unit within a network, system, or data structure that serves as a connection point, device, or data element. In computer networks, a node can be any physical device such as a computer, router, or switch that sends, receives, or forwards information. In data structures like linked lists or trees, a node represents an individual element containing data and links to other nodes. Nodes are essential for enabling communication, data organization, and efficient processing within various technological environments.