A repeater is used to extend a network connection over long distances. A repeater receives a signal, regenerates it, and then resends the signal out another interface. It does not make any forwarding decisions to determine which connection the signal must go to.
Common uses of repeaters are to extend the network for copper or fiber connections. Repeaters can also convert one physical type to another. For example can take in Ethernet over fiber and output Ethernet over copper.
