1. （活动的）中心，核心
You can describe a place as a hub of an activity when it is a very important centre for that activity.

2. （轮）毂
The hub of a wheel is the part at the centre.

3. 航空枢纽;中心机场
A hub or a hub airport is a large airport from which you can travel to many other airports.

4. （网络）集线器
A hub is a device for connecting computers in a network.

1. the central part of a car wheel (or fan or propeller etc) through which the shaft or axle passes

2. a center of activity or interest or commerce or transportation
a focal point around which events revolve

e.g. the playground is the hub of parental supervision
the airport is the economic hub of the area