What type of device is primarily used to connect different networks together and route traffic between them?

The primary function of a router is to connect different networks and manage the traffic that flows between them. Routers operate at the network layer of the OSI model and are responsible for determining the best path for data packets, enabling communication between multiple devices across different networks. They use routing tables and protocols to direct packets effectively, making decisions based on IP addresses.

In contrast, devices like switches and bridges operate primarily within a single network. Switches facilitate communication within a local area network (LAN) by filtering and forwarding data only to the intended recipient within that local network, without interfacing with external networks extensively. Bridges serve a similar purpose by connecting different segments of a LAN and can also filter traffic; however, they do not perform the routing function needed to connect separate networks.

Hubs, on the other hand, are basic networking devices that transmit incoming data packets to all connected devices on a network segment without differentiating between them. This lack of intelligence means they do not manage traffic or route packets between different networks.

Therefore, the router is the correct answer as it is specifically designed for inter-network communication, fulfilling the crucial role of routing traffic across different networks, unlike the other devices listed.