High seas refer to the open ocean or any part of the sea beyond the jurisdiction of the coastal state. While it's a commonly used term, there are several synonyms for high seas that can be used in writing or conversation. Some of the alternatives include open water, deep sea, blue water, offshore waters, and vast ocean. Other phrases that convey a similar meaning include "the great beyond," "unchartered waters," and "the open expanse of the sea." Using these synonyms can diversify your language and bring more nuance to your writing, while accurately conveying the meaning of the high seas.