Actually, I have heard of it. As a Canadian based trucker, illegal movement of goods point to point in the US was defined by the term.
Even moving an empty trailer from one point to another falls under cabotage rules. The only way moving an empty trailer point to point is allowed is if it was either live unloaded at the beginning point ( load originating in Canada) or live loaded at the end point with a load destined directly to Canada.
This was a bit of a logistical nightmare as a lot of the major customers had a bunch of our trailers in the yard and many moves were drop and hook, so if you were doing a drop and hook on the home bound, it had to be live unload on the outbound.