Legal capacity (competency): The right and ability to manage one’s own affairs (usually starting at age 18 in most states).

Legal incapacity (incompetency): The inability to manage one’s own affairs because of injury or disability, as determined by a legal proceeding.

Clinical incapacity to make health care decisions: The inability to understand the significant benefits, harms, and alternatives to proposed health care and to make and communicate a health care decision, as determined by a qualified doctor or other health care professional.

Advance directives: Documents or other recordings such as a living will or a health care power of attorney that communicates a person's wishes about health care decisions.

Living will: A document, sometimes called a medical directive, that expresses a person’s wishes regarding future medical interventions and end-of-life care when the person no longer has the capacity to make health care decisions.

Health care power of attorney: A document that legally appoints someone else to make health care decisions on a person's behalf in the event the person no longer has the capacity to make health care decisions. The person appointed may be called a health care agent or proxy, health care representative, or other name depending on the state.