The "Simple Security Property" is a fundamental concept in computer security, particularly in the context of access control models like the Bell-LaPadula Model. It ensures that a subject (like a user or process) at a certain security level cannot read data at a higher security level. This prevents unauthorized access to sensitive information. This property is crucial for maintaining confidentiality in systems that handle classified information. By enforcing this rule, organizations can protect their data from being exposed to individuals who do not have the necessary clearance, thereby reducing the risk of data breaches and leaks.