There are two primary types of hubs in the computing world: 1) network hubs and 2) USB hubs.
1. Network hub
A network hub is a device that allows multiple computers to communicate with each other over a network. It has several Ethernet ports that are used to connect two or more network devices together. Each computer or device connected to the hub can communicate with any other device connected to one of the hub's Ethernet ports.
Hubs are similar to switches, but are not as "smart." While switches send incoming data to a specific port, hubs broadcast all incoming data to all active ports. For example, if five devices are connected to an 8-port hub, all data received by the hub is relayed to the five active ports. While this ensures the data gets to the right port, it also leads to inefficient use of the network bandwidth. For this reason, switches are much more commonly used than hubs.
2. USB hub
A USB hub is a device that allows multiple peripherals to connect through a single USB port. It is designed to increase the number of USB devices you can connect to a computer. For example, if your computer has two USB ports, but you want to connect five USB devices, you can connect a 4-port USB hub to one of the ports. The hub will create four ports out of one, giving you five total ports. The USB interface allows you to daisy chain USB hubs together and connect up to 127 devices to a single computer.
Some USB hubs include a power supply, while others do not. If you're connecting basic devices like a mouse, keyboard, and USB flash drive, an unpowered or "passive" USB hub should work fine. However, some peripherals, like external hard drives and backlit keyboards, require additional electrical power. In order for these types of devices to function through a USB hub, you may need use a powered or "active" hub that provides 5 volts of power to connected devices.
Updated: June 27, 2015