A ward is a minor that can't be with their birth parents (usually due to their death), so the minor is assigned by the court to another adult called their guardian.

A court may take responsibility for the legal protection of an individual, usually either a child or incapacitated person, in which case the ward is known as a ward of the court or a ward of the state.

In Rain

Rain became Fara's ward after her mother (Liriel Flaherty) died and her father (Marcus Flaherty) walked out on the family. Those events happened before the start of the story.