Mental disorder is when something is not quite right in our minds. It can mean that we don't feel like we usually do and our feelings, thoughts, or behaviors may be upsetting to us or to other people. For example, some people have a hard time controlling their emotions, so they may get really angry or scared very easily. Or someone may have a condition that makes it hard to concentrate or remember things. Mental disorders like these can be tough to deal with and might need special help from a doctor.