A node is a fundamental unit in various fields, including computer science and networking. In a network, a node can represent any device that connects to the network, such as a computer, printer, or router. Each node can send, receive, or forward data, contributing to the overall communication within the network. In data structures, a node is an element that contains data and may link to other nodes. For example, in a linked list, each node holds a value and a reference to the next node, allowing for efficient data organization and manipulation. Nodes are essential for building complex structures like trees and graphs.