The hub is a complex island in which the Auction House and Bazaar are. This is the island in which most players will do trading and miscillaneous item gathering, as well as begin Slayers. The hub has a lot of NPCs (Non-Player Characters) with specific tasks to carry out for the player, including:
It is the center island that branches out to all the other islands.
Image taken by me, created by the Hypixel Team