An Ethernet switch is a device used to build a network connection between attached computers. The Ethernet switch understands the incoming packets' destination and will send any data packet only to its destination port, thus limiting the number of collisions (data sent at the same time). Unlike a router that is considered part of layer 3 in the OSI model, an Ethernet switch is part of layer 2, the data link layer.
An ethernet router is a device that forwards data packets between computer networks, essentially performing the "traffic directing" functions on the Internet. When a data packet comes in one of the data lines, the router reads the address information in the packet and directs the packet to the correct network on a different data line. The most familiar type of routers are home and small office routers that simply pass data between the home computers and the Internet. More sophisticated enterprise routers connect large business or ISP networks to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone.