A charter is a formal document describing the rights, aims, or principles of an organization or group of people.

A charter plane or boat is one which is hired for use by a particular person or group and which is not part of a regular service.

If a person or organization charters a plane, boat, or other vehicle, they hire it for their own use.

If you describe a decision or policy as a charter for someone or something you disapprove of, you mean that it is likely to help or encourage them.