Similar in nature to a database table and object containing record data, in Salesforce CRM, custom settings can be thought of as a database table that contains configuration data.
There are two types of custom settings—there is the List type and there is the Hierarchy type. Both types are traditionally referenced from code to allow developers to create settings data, which is cached within the application.
List custom settings are referenced in code only and allow developers to store and access a reusable set of static data at the organization level.
Hierarchy custom settings are referenced in the code and can also be referenced within the declarative setup, such as formula fields, validation rules (covered in Chapter 5, Managing Data in Salesforce CRM), and Process Builder and Workflow Rules (covered in Chapter 7, Implementing Business Processes in Salesforce...