Critical Race Theory (CRT) is an academic discipline (though it is really interdisciplinary in nature) that holds that institutionalized racism is just as important as, or more important than, overt and individual racism.
CRT believes that racism is still a powerful force in America even though overt racism is very much less common than it once was. CRT theorists argue that racism is inherent in many parts of the American power structure. They believe that our institutions are set up in a way that reproduces white privilege and keeps white people in power. In this way, our system is inherently racist (they say) even if individual racism is no longer common.