A more thorough explanation:

Adult adoption is a legal process where one adult adopts another adult as their child. This creates a parent-child relationship between the two parties, even if they are not related by blood.

Unlike traditional adoption, adult adoption does not require the determination that the child is an orphan or has been abandoned. Instead, it is a voluntary process that can be initiated by either the adoptive parent or the adult being adopted.

For example, an adult may choose to be adopted by their step-parent to formalize their relationship and gain legal rights and responsibilities as a child. Another example is when an elderly person without children chooses to adopt a younger adult to ensure they have someone to care for them in their old age.

Adult adoption is different from legitimation, which is the process of establishing a legal relationship between a father and child born out of wedlock. It is also different from fostering, which is a temporary arrangement where a child is placed in the care of another adult.

Overall, adult adoption is a way for two adults to create a legal parent-child relationship, even if they are not related by blood.