Horizontal inequality means that some groups of people do not get the same opportunities and benefits as other groups of people. For example, some people may not have access to the same kind of education, healthcare, and jobs as other people just because they are from a different gender, race, religion, or some other group. This means that some people are not treated the same and don't get the same kind of chances as others. It's unfair and can leave some people feeling left out.