A USB hub is a device that expands a single USB port into multiple ports, allowing you to connect several devices at once. It is commonly used with computers and laptops to connect peripherals like keyboards, mice, printers, and external hard drives. USB hubs can be powered or unpowered. Powered hubs have their own power supply, which allows them to support more devices and provide additional power to connected devices. Unpowered hubs rely on the power from the computer's USB port, making them suitable for low-power devices.