Geez its difficult to ans w/o having it looks like a cut-and-paste as it relates to their definitions. i will try:
HDI is short for Human Development Index. It is a measure developed by the United Nation to measure a country’s average achievements in health, education and income.
IHDI is Inequality-adjusted Human Development Index. It is similar to HDI but has an extra adjustment for inequality. If only a small portion of ppl have great comfort and wealth, a high HDI does no good for the general population. By adding the inequality adjustment, IHDI gives a better measure of a country for its whole population.