Crispy™ Define: "Hub based"

[Metro]

I think of a hub as some sort of connective tissue that binds quests/areas together. Tomb Raider 4's levels are often hub based, especially the Alexandria levels (which has hubs within hubs). Thief 3 connects its missions through the hub of the city streets level. Deus Ex is heavily hub based.

In those games, the hub level is a level from which you access all the other levels. TR4's Alexandria is a great example, there are several levels to explore and they are all accessed by exploring different ruins located on the same map.
In Deus Ex, Hong Kong is the most well-regarded hub level.

This. Hub-type games are distinct from open-world games. Using a hub gives the game a patina of an open world but usually there is little to no backtracking involved making hub-type games generally mission oriented. While open world games may have a dominant/center city or place of trade/training/whatever, that doesn't make them hub-type games as you can travel from pretty much any area to any other area without the need to go back to the hub. Although this is subject to tech/data limitations, e.g., how World of Warcraft requires you to go through certain access points to get from one expansion's content to the next.