A router is a network device which is connected between network subnets and knows where to send a packet it received.\nWhen you use your browser to look at Yahoo!, for example, HTTP data packets from your PC travels to Yahoo  by going from router to router until they reach Yahoo! server. Each router is a "hop" on the way and each knows where to send your packet next.\nA response from Yahoo goes back through the network in similar way (not necessarily through same networks).\n\nYou may have a router box at home, which usually knows about your home subnet and your ISP subnet.\nCisco builds "big iron" routers which are the backbone of the internet.
What is a router?