/ˈnæʃənl ˈfrʌntɪər/ – Phrase
Definition: biên giới quốc gia.
A more thorough explanation: The legal English definition of the term “national frontier” refers to the border or boundary that separates one country from another, marking the territorial limits of a nation. It is the outermost line or limit of a country’s territory, beyond which the jurisdiction and sovereignty of that nation do not extend. The national frontier is a significant concept in international law and relations, as it defines the extent of a country’s authority and control over its territory.
Example: The government deployed additional troops to secure the national frontier against potential incursions by foreign forces.