Black soil, commonly known as Regur soil, is a type of soil that is found in several parts of India. It gets its name from its high fertility, dark color, and ability to retain moisture. Option 1, Khadar Soil, is incorrect as Khadar soil refers to alluvial soil found in river valleys and is different from black soil. Option 2, Bangar Soil, is also incorrect as it refers to older alluvial soil found away from river valleys and is again different from black soil. Option 3, AUuivial Soil, seems to be a typographical error and is not a valid term. Therefore, the correct answer is option 4, Regur soil, which is the commonly used name for black soil due to its unique characteristics and agricultural importance.