<p><strong>Noun</strong></p><ul><li>the part of a country that borders another country; boundary; border.</li><li>the land or territory that forms the furthest extent of a country's settled or inhabited regions. Often frontiers.</li><li>the limit of knowledge or the most advanced achievement in a particular field: the frontiers of physics.</li><li>an outer limit in a field of endeavor, especially one in which the opportunities for research and development have not been exploited: the frontiers of space exploration.</li><li>Mathematics. boundary (def 3).</li></ul><p><strong>End of Response</strong></p>