Hello Peter
That’s a good question, and it is true that terminology can sometimes be confusing. The term hub is used in various situations, and its meaning must be identified based on the context.
A Layer 2 hub is a device that physically looks like a switch, as shown below. It does the same thing as a switch, that is, it interconnects network devices by having them plug into the Ethernet ports, and allows them to communicate with each other.
The difference however is how they perform this communication. Hubs retransmit anything they receive out of all their ports while switches selectively retransmit frames based on the intended destination, thus being more efficient. More about these differences can be found at the following lesson:
Now as far as a hub router used in a hub and spoke topology, or in a DMVPN scenario, this is a different thing entirely. Such a topology is like a bicycle wheel or an old fashioned wagon wheel. These wheels have two components: spokes, and hubs. The hub is the place where all of the spokes converge.
Notice the similarities in the following two pictures of a wheel and a hub and spoke topology:
The term hub is used to refer to the router that is in the center of the topology, and spokes are used to refer to the routers that are connected to the hub router.
So in the case of a layer 2 hub, the term is used to refer to a specific type of device, while the term hub router, refers to a part of a particular topology.
I hope this has been helpful!
Laz