The CIA Triad is a venerable, well-known model for security policy development, used to identify problem areas and necessary solutions for information security.
Protecting your most sensitive information from unauthorized access.
Protecting confidentiality hinges upon defining and enforcing appropriate access levels for information. Doing so often involves separating information into discrete collections organized by who should have access to it and how sensitive it is.
Protecting data from modification or deletion by unauthorized parties, and ensuring that when authorized people make changes that shouldn't have been made the damage can be undone.
Some data should not be inappropriately modifiable at all, such as user account controls, because even a momentary change can lead to significant service interruptions and confidentiality breaches.
Systems, access channels, and authentication mechanisms must all be working properly for the information they provide and protect to be available when needed.