What does "transit" mean in the context of an MPLS network? We've had a quote submitted by an ISP to change our current numerous Internet connections over to a managed MPLS network however on the quote it is mentioned that it includes "X mb of transit in our data centre". What exactly does that mean? I've searched online for "MPLS transit" etc. but can't seem to find an explanation of what it means?

We queried it and were told that it's the amount of external traffic permitted. Internal traffic isn't counted.