The transport activity is, in the same time, very specific from the technical and organizational point of view, and closely linked with all other agricultural, manufacturing and commercial industries. The various notions of field, sector, industry, industrial channel, eventually system of freight, have a different content, to which correspond different economic parts in the productive system. This paper tries to make these notions more clear, and to measure their corresponding weights. The public freight sector appears to be the emerged part of a much larger freight channel requiring, in France, several millions of jobs! The distinction between these various notions is a scientific clarification, it has also more immediate consequences, as it helps designating the relevant field and the legitimate economic actors likely to take part to the conception and the implementation of public transport policies.