Simply, internal migration refers to the movement of people within a country. So, internal migration can be defined as the human migration within one geopolitical entity, usually a nation.
Simply, the movement of people from one country to another is called international migration. So, external migration refers to change of residence over national boundaries.
According to the statistics of 2068, the Terai region of Nepal covers more than 50% of the total population of Nepal.
The main reasons for the increment in a population of Terai region are the attractions and facilities of trade, agriculture, employment etc.