I can't find it right now, but there was a time when HubPages offered a diagram to point out why Hubs are called what they are. The diagram showed one circle at the center, and around that circle were other circles, connected with a line to the one in the center.
The circle in the center represented the subject of the article/writing. The "offshoot" circles represented other material related to the subject and presented with the use of the capsules such as links, videos, etc. So, there's the one core subject that is the article, itself; and then there's the "spin-off" information associated with the core subject.