The CIA TRIAD is the foundation of information security, and is made up of 3 principles.
Information is not disclosed to individuals or devices unless they are authorized to. For example, student's grades can only be accessed by authorized individuals, such as teachers.
Information/Information systems or a component of a system that has not been modified in any unauthorized manner. For example, student's grades are accurate and have not been modified by unauthorized users.
Information is availiable and useable on demand. For example, student's grades can be viewed by the students and the principal and modified by the teacher.