What is the meaning of Body_mass_index?

A statistical measure of the weight of a person scaled according to height, used to estimate if a person is underweight or overweight. BMI units are defined as ${\displaystyle \mathrm {kg} /\mathrm {m} ^{2}}$ ≈ ${\displaystyle \mathrm {703*lb} /\mathrm {in} ^{2}}$.

Source: wiktionary.org