The USB hub - Generally.
A USB hub is a very convenient device which lets you expand one USB port to multiple USB hub ports. The USB hub comes in a variety of sizes, shapes and designs, however they all have the same function of expanding a USB hub port.
The typical USB hub has four, seven or ten ports however some USB hubs have even more ports. USB hubs with up to four ports are usually bus-powered, which means that they draw power from the computers USB port and does not need an external power supply. USB hubs with four or more ports are usually powered by an external power adapter. Keep in mind that bus powered USB hubs generally only should be used for connecting smaller USB hub devices such as mice, keyboards, mp3 players, memory drives and similar due to its limited bus-powered USB hub power supply.
Externally powered USB hubs can be used for larger devices which draw more power such as USB hub scanners, printers and hard drives.
Another feature to look for when shopping for a USB hub is if the USB hub is a USB 2.0 or USB 1.1 hub. Most modern USB hubs are compatible with both USB 1.0 and USB 2.0.