Simply put, a health disparity is the poorer health one group has compared to another. LGBT people have more depression and anxiety than non-LGBT people, when you compare the groups’ averages. African-Americans and Latin@s are far more likely than white people to contract HIV/AIDS. An important aspect of health disparities is that “[f]or people who belong to mulitple communities that experience health disparities, these disparities do not simply add up: They multiply.” Thus, African-American LGBT people, on average, have poorer health than either white LGBT people or African-Americans who aren’t LGBT.
Health equity is the opposite concept: rather than focusing on the differences, health equity focuses on where we want to be: attaining the highest level of health for all people. A good short article on these concepts, with multiple links, is available at http://thinkprogress.org/lgbt/2012/04/27/472826/health-disparities-lgbt/