Router is a layer 3 device which works on network layer of OSI model which connects two different networks and it identifies network devices based on their IP addresses.
The Routers are the devices used for connecting local network to the other local network/s. They are generally located at the gateway where two or more than two networks connect.
Switch is a layer 2 device which works on data link layer of OSI model, it communicates by using frames and it identifies network devices on the basis of MAC addresses or physical addresses.
System Switching Board (SSB) and Forwarding Engine Board (FEB) are the two different router models used for the control board functionality.
An aggregate route is the second form of a locally configured route within the JUNOS software.