In the context of EDI, the term Hub usually refers to the buyer in a B2B transaction. The seller is referred to as a Spoke.

Merriam-Webster Online Dictionary
hub (noun)
the central part of a circular object (as a wheel or propeller)
a) a center of activity - focal point
b) an airport or city through which an airline routes most of its traffic
c) a central device that connects multiple computers on a single network
a steel punch from which a working die for a coin or medal is made