This is the definition of hub:
The central part of a wheel, rotating on or with the axle, and from which the spokes radiate.
A place or thing that forms the effective center of an activity, region, or network.
I was wondering what are the possible meaning of the word when it is included in the name of a website. Because it seems to me that any website can act as a 'hub' (a network/activity site).
(One example is GitHub).