A node is a fundamental unit in various fields, including computer science, networking, and biology. In computer networks, a node refers to any device that can send, receive, or forward data, such as a computer, printer, or router. Each node has a unique identifier, allowing it to communicate with other nodes within the network. In the context of graph theory, a node is often called a vertex and represents a point where lines or edges meet. Nodes can represent various entities, such as cities in a transportation network or individuals in a social network, facilitating the study of relationships and connections between them.