The Human Development Index (HDI) is a way to measure how a country or area is developing, or improving. It looks at three main areas: health, education, and living standards. The higher the HDI is, the better the country is doing in those three areas. The HDI takes into account things like how many years people are living, the number of people who are going to school and finishing school, and how much money people have to buy things they need. So, if the HDI is high, that means people in the country or area have longer lives, more people are educated and have enough money to buy the things they need.