A more thorough explanation:

Compos mentis is a Latin term that means "having control of one's mind." It is used to describe people who are mentally competent and capable of managing their own affairs.

For example, a person who is compos mentis is able to make decisions for themselves, understand the consequences of their actions, and communicate their thoughts and feelings clearly.

The opposite of compos mentis is non compos mentis, which refers to someone who is not of sound mind and is unable to manage their own affairs.

Overall, compos mentis is an important concept in legal and medical contexts, as it helps to determine a person's ability to make decisions and take responsibility for their actions.