Horizontal Privilege Escalation occurs when a user gains access to resources or data that belong to another user at the same privilege level. This type of security breach typically happens in systems where user permissions are not properly enforced, allowing one user to exploit vulnerabilities to access another user's information. This can lead to unauthorized data exposure, privacy violations, and potential data manipulation. Organizations must implement strong access controls and monitoring to prevent such incidents, ensuring that each user's permissions are strictly defined and enforced to protect sensitive information from unauthorized access.