Hubs are network devices with multiple physical ports whose purpose is to receive a signal from the physical wire on one port and
repeat it blindly to all other ports on the hub. When more than one hub is used, the message is broadcasted from one hub to the next and to all ports off all hubs. The total set of communications links connected via multiple repeaters is called a collision domain. A collision domain is the set of all communications links over which any single network message is broadcasted at the physical layer. Hubs work well for small networks where there are only a few devices. Connecting multiple hubs creates a large collision domain which can impair network performance when the number of hosts is large. Ethernet is a broadcast network technology and ethernet hubs can be used to connect multiple devices.
Hubs have nearly passed out of use in networking as network speeds have increased and the need for ever higher data rates grows.