A router is a networking device that forwards data packets between computer networks. It functions by determining the optimal path for data traffic across interconnected networks, utilizing routing tables and Internet Protocol (IP) addresses to identify the best route from a source network to a destination network. Unlike a simple switch, which operates within a single local network segment, a router operates at the network layer of the OSI model, managing the flow of information across dissimilar networks. These devices are fundamental components of the internet infrastructure, allowing disparate systems to communicate and access shared resources globally.