Dear Sambhaji Dnyaneshwar Shinde NDVI is normalized Difference vegetation index which tells about the (NIR-R)/(NIR+R), it ranges from 0 to 1. greenness index.
NDVI is nothing but the ratio of (NIR-R/NIR+R), as vegetation is reflecting more amount of NIR radiation. It is quite useful to Assess Drought as well as Vegetation health. It also used to assess impact of Irrigation project on Agriculture. Besides this it also applicable in Soil Erosion Modelling as Cover Management Factor calculation and many more.