A Latin term meaning for the purposes of the lawsuit. For example, a guardian "ad litem" is a person appointed by the court to protect the interests of a minor or legally incompetent person in a lawsuit.
From the Latin, meaning "for the lawsuit" -- that is, for purposes of the current legal action. A guardian ad litem is a guardian appointed by the court to act on behalf of a minor or incompetent person. (Wex)
Ad litem is a term used in law to refer to a party appointed by a court to act in a lawsuit on behalf of another partyâ€”for instance, a child or an incapacitated adultâ€”who is deemed incapable of representing themselves. An individual who acts in this capacity is called a guardian ad litem. This term is no longer used in the United Kingdom since the passage of the Children Act 1989, which established the role of children's guardian instead.