Custom settings are a type of custom data that can be used to store secret data with an ability to specify which profiles and users can access which secrets. Custom settings can store data in a hierarchical structure, which allows the developer to set different values for different levels of access, such as organization, profile, or user. Custom settings can also be encrypted using the Protected Custom Settings feature, which prevents the data from being exposed in the user interface, the API, or Apex code. By using custom settings, the developer can store the secret data securely and control the access to the data based on the user's profile or identity. Reference: [Custom Settings], [Protected Custom Settings]