What is the difference between possession in fact and possession in law?

[Jurisprudence] The conception of possession has evolved through a long course of time. In the beginning, it was only a fact; it meant physical control over a thing. Later on, this fact started receiving recognition and protection by law. Thus possession included a physical relation with the object as well as its recognition by law. Possession in fact and possession in law are co-terminus but is not necessarily available at the same time, possession may be in fact not in law or possession may be in law but not in fact.