mare liberum

from WordNet (r) 3.0 (2006)

mare liberum
    n 1: (free sea) a navigable body of water to which all nations
         have equal access

from The Collaborative International Dictionary of English v.0.48

mare liberum \mare liberum\ n. [L., free sea.]
   A navigable body of water to which all nations have equal
   access; the opposite of {mare clausum}.
   [WordNet 1.5]