high seas 
plural noun (the high seas)
The open ocean, especially that not within any country’s jurisdiction: drift-net fishing on the high seas it has seized ships on the high seas and has shot down planes in international airspace...
- In customary law, only the flag state has jurisdiction to enforce regulations applicable to vessels on the high seas.
- Piracy has flourished on the high seas for as long as maritime commerce has existed between states.
- He joined Scindia Steam Navigation as a sea cadet and sailed the high seas for the next 10 years.