hubs

A hub is a small rectangular box often constructed mainly of plastic. A hub includes a series of ports that each accept a network cable. They contain four or sometimes five ports (the fifth port being reserved for 'uplink' connections to another hub or similar device). It receives its power from an ordinary wall outlet.
A hub joins multiple computers (or other network devices) together to form a single network segment.
On this network segment all computers can communicate directly with each other.
Small hubs network four computers.
Ethernet hubs are by far the most common type but hubs for other types of networks such as USB also exist.
Larger hubs contain eight 12 16 and even 24 ports.
Hubs are also known as multiport repeaters or concentrators.
They connect various segments and act like a repeater.
This enables every segment to receive signals from any other segment.