I/O expandersare a type of computer hardware that allows more than one device to connect to a single port on a computer.
The expander connects to a single spot, but has multiple connections for other devices. Such expanders offer the advantage of allowing more devices of a particular port type to be used at the same time. This commonly used with USBs and ethernet ports.
There are two main types of I/O expanders: internal and external.
These have a connection inside the computer, typically on the motherboard, and the only part the user can see is the expansion plate which houses the ports to which they can connect more devices.
An external expander plugs into an existing port introducing multiple new places to connect. When not part of a computer system, these devices are commonly known as splitters.