mare liberum
Concise Oxford English Dictionary © 2008 Oxford University Press:
mare liberum /ˌmɑːreɪ ˈliːbərʊm, ˈlʌɪbərəm/
▶noun (pl. maria libera /ˌmɑːrɪə ˈliːbərə, ˈlʌɪbərə/) Law the sea open to all nations.
– origin L., lit. ‘free sea’.
'mare liberum' also found in these Oxford entries:

