What is adverse impact?

If you're looking for a definition of "adverse impact", in general terms, it means there was a negative impact vs. an expected positive impact on a thing. For example, a few intentions of the president's plan to provide free health care for all mothers and children in the U.S. is healthier kids, and families that can afford the basics. A few potential adverse impacts of the presidents plan are higher taxes and people having more children because they know they will have free health care, which in turn increases the population, potentially increases the illiterate population, potentially increasing the violent crime rate, potentially increasing the burden on the soon-to-be-bankrupt social security system, etc, etc.