The phrase "over sea" refers to a location across the sea or beyond the sea. It can be replaced by several synonyms such as overseas, across the ocean, beyond the water, across the sea, over the water, transoceanic, and international. All these synonyms relate to a location that isn't reachable by land transport. They are mostly used to indicate that someone or something is located in another country or continent. The use of such synonyms can add variety to the language and make the writing or speaking more interesting and engaging.