Mutism is a communication disorder characterized by an individual's inability or unwillingness to speak in certain situations despite having the ability to do so. It can be classified into different types, such as selective mutism, where a person speaks in some contexts but not others, often seen in children, and total mutism, where a person does not speak at all. This condition can be linked to anxiety, trauma, or developmental issues. Treatment often involves therapy to address underlying causes and improve communication skills.