"RES COMMUNES" - THINGS COMMON TO ALL
It may be recalled that "Res Nullius" are physical things which "have not or have never had" an owner. Res nullius is a category of "things." The property status of such a thing while it remains in a wild, unappropriated, state is "res communes," or a "thing common to all."
The opinion in Geer v. Connecticut, 161 U.S. 519 (1896), provides an excellent summary of the status of "res communes":
[Potheir, "Trait e du Droit de Propriet e, No. 21:] 'The first of mankind had in common all those things which God had given to the human race. This community was not a positive community of interest, like that which exists between several persons who have the ownership of a thing in which each have their particular portion. It was a community, which those who have written on this subject have called 'a negative community,' which resulted from the fact that those things which were common to all belonged no more to one than to the others, and hence no one could prevent another from taking of these common things that portion which he judged necessary in order to subserve his wants. Whilst he was using them, others could not disturb him; but when he had ceased to use them, if they were not things which were consumed by the fact of use, the things immediately re-entered into the negative community, and another could use them. The human race having multiplied, men partitioned among themselves the earth and the greater part of those things which were on its surface. That which fell to each one among them commenced to belong to him in private ownership, and this process is the origin of the right of property. Some things, however, did not enter into this division, and remain, therefore, to this day, in the condition of the ancient and negative community.'
"Referring to those things which remain common, or in what he qualified as the negative community, this great writer says:
'These things are those which the jurisconsults called 'res communes.' Marcien refers to several kinds,-the air, the water which runs in the rivers, the sea, and its shores. ... ' [Emphasis mine.]
Things "res communes" remain "public domain" in the community at large - avaiable for use (usufruct) by any member of the community. These resources are generally incapable of private appropriation by their dynamic nature or definition, such as free flowing water, air, and light.