The term New World is often used to mean the majority of Earth's Western Hemisphere, specifically the Americas. The term gained prominence in the early 16th century, during Europe's Age of Discovery, shortly after the Italian explorer Amerigo Vespucci concluded that America (now often called the Americas) represented a new continent, and subsequently published his findings in a pamphlet he titled Latin: Mundus Novus. This realization expanded the geographical horizon of classical European geographers, who had thought the world consisted of Africa, Europe, and Asia, collectively now referred to as the Old World, or Afro-Eurasia. The Americas were thus also referred to as "the fourth part of the world".
Why was America called the New World?
In the past, the major civilizations were unaware of the existence of America. Since their world view consisted of Europe, Africa and Asia, the finding of an entire continent of the Americas was a major geographical perspective to the people of the era. They referred to America as the New World.