A USB hub is a device that expands a single USB port into multiple ports, allowing you to connect several devices at once. This is particularly useful for computers and laptops that have limited USB ports, enabling users to connect items like keyboards, mice, printers, and external drives simultaneously. Most USB hubs are powered, meaning they can provide additional power to connected devices, which is essential for high-energy items like external hard drives. They come in various shapes and sizes, including portable models for travel and larger stationary hubs for desktop use, making them versatile for different needs.