What is Actio In Rem?

Legal Definition
In the civil and common law. An action for a thing; an action for the recovery of a thing possessed by another. Inst. 4, 6, 1. An action for the enforcement of a right (or for redress for its invasion) which was originally available against all the world, and not in any special sense against the individual sued, until he violated it See In Rem.
-- Black's Law Dictionary
Legal Definition
An action against a thing; for the recovery of a thing or the establishment of a right independent of contract.
-- Ballentine's Law Dictionary