Routers
A device used to connect networks of different types, such as those using different topologies and protocols.
Gateways
A gateway is a device used to connect networks using different protocols.
In order to communicate with a host on another network, an IP host must be configured with a route to the destination network. If a configuration route is not found, the host uses the gateway (default IP router) to transmit the traffic to the destination host.
So whats the differnce?
Info taken from http://www.studynotes.net/indnet.htm