Not a stupid question at all.
Well, I hope that I was able to shed a little light on what a switch was in your other post. In that case, a router is a networking device (hardware or software) that is able to communicate between 2 or more different networks. A router will receive a network packet and determine, by the packet's header information, if the packet should be, ignored, passed along, or edited and then passed along. Also, if it does need to pass along the packet, it will determine (given it's ever-changing routing tables) the best route to it's destination. Routers are used everyday to make the internet possible. I know that this may not be as informative as you may have hoped.....but it's a starting block.
-Mike