The correct answer is option 4 - Black cotton soil.

Black cotton soil, also known as regur soil, is a type of soil that is commonly found in certain regions of India. It is characterized by its high clay content and dark color.

Option 1 - Laterite soil: Laterite soil is a type of soil that is found in tropical and subtropical regions. It is rich in iron and aluminum oxides and is generally red in color. It is not the same as black cotton soil or regur.

Option 2 - Deltaic soil: Deltaic soil is a type of soil that is found in river deltas. It is formed by the sedimentation of river deposits and is generally fertile. It is not the same as black cotton soil or regur.

Option 3 - Red soil: Red soil is a type of soil that is characterized by its red color. It is formed from weathered rocks and has a good drainage system. It is not the same as black cotton soil or regur.

In conclusion, the term "regur" is used to refer to black cotton soil, which is characterized by its high clay content and dark color.