A router is a special purpose computer, that allows to connect to multiple computer networks.
Routers are both hardware & software devices.
|Figure: Routers in computer networking|
Router can connect network segments, and filters and isolate traffic.
Unlike a bridge, a router can connect networks that uses different technology, addressing methods, media types, frame format speeds.
Routers operator at "Network Layer" in OSI model.
|Figure: Routers in Networking|