Final answer:
Validation rules are executed whenever a record is saved in Salesforce. They are not page layout or Visualforce dependent and can apply to all interfaces in Salesforce. Validation rules are written using Salesforce Object Query Language (SOQL).
Step-by-step explanation:
Validation rules in Salesforce are executed whenever a record is saved. These rules are defined at the object level and are enforced by the database. They are not page layout or Visualforce dependent, meaning they can apply to all interfaces in Salesforce, including standard and custom layouts, Visualforce pages, and even APIs.
Validation rules are written using a formula language called Salesforce Object Query Language (SOQL). This language allows you to define conditions that must be true for a record to be saved. For example, you can create a validation rule that requires the 'Email' field to be populated if the 'Contact Method' field is set to 'Email'.
When a record is saved, Salesforce evaluates all the validation rules defined for that object. If any of the rules fail, an error message is displayed to the user and the record is not saved. The error message can be customized to provide meaningful information to the user about why the record cannot be saved.