A hub is a centrally located, high traffic area - like an airline hub - people coming, connecting, and going.
In networking, a hub is not a specific piece of computer equipment. It is a type of computer equipment. If you walked into a computer parts store and said you needed a hub, they would most likely know what you are talking about, but they would also know that you know diddley about computers.
There are a few kinds of hubs; the three most common are repeaters, switches, and routers. I won't delve into the difference between the last two here, but I would like to educate you on the difference between a repeater and a router.
Let's say you are home in your house and you see something funny on TV (amazing!). You want to tell your spouse two rooms down about it. So you shout into the next room where your eight kids are. The kid closest to the door is the only one that hears you, and he shouts the message to the next room, but in doing so, lets all the other children hear the message. In the next room, where your spouse and his/her friends are talking, everyone in the room hears the relayed message (and laughs - what a funny joke).
You are the computer. Your oldest child is the repeater, and the other children are other computers. Your spouse and friends are other computers as well. This is how a repeater works.
Now if we make your repeater-child a router instead, he would hear the message and know it was meant for mom's ears only, and he would go tell her privately without any of the other children or friends being privvy to that information.
The advantages of a router are privacy and efficiency. The advantage of a repeater is simplicity, with which comes a smaller price tag.
A repeater works on the hardware level. In other words it doesn't try to interpret any of the signals that come its way, it merely passes them on. This is why it has been called a "dumb hub", and is what you will get if you ever ask for a "hub" at a store. Simplicity, no processing power needed, no time taken.
But a router stops each signal, tears it apart, examines the address information, throws it all back together, and sends it on its way.
If you ever question whether you have a repeater or a router, you have a repeater. Repeaters are great for home networking and on small or large LANs. The topology of a network might include one router towards the center of the network with little repeaters on the outskirts - you don't want every piece of traffic on your LAN going through your router unless it is a very small LAN.