Or you can read the hub definition from whatis.com.
A hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub usually includes a switch of some kind. (And a product that is called a “switch” could usually be considered a hub as well.) The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data is forwarded from the place where data comes together.
Here’s a photo of a USB hub. You plug one end into your computer and then you can plug all your USB devices into the hub. It’s kind of like a power strip for USB devices.