Salesforce Certified Identity and Access Management Practice

A "Custom Domain" in Salesforce refers to a branded subdomain that allows organizations to create personalized URL access for users accessing Salesforce applications. This feature helps enhance branding and provides a more coherent user experience, as users can access their Salesforce instance through a URL that reflects the organization's identity, such as `https://yourcompany.my.salesforce.com` instead of a generic Salesforce URL.

Using a custom domain also allows for improved security measures, as it enables the use of enhanced authentication methods and supports single sign-on (SSO) experiences. Furthermore, it can make your applications more recognizable and trustworthy to users, thus fostering better engagement and usability.

The other choices do not accurately describe what a Custom Domain is. The feature for internal communication between users relates more to collaboration tools within Salesforce rather than URL customization. An application for external user logins is part of the broader identity and access management framework but does not define Custom Domains. Lastly, a database for securely storing user credentials pertains to data security practices rather than the concept of a Custom Domain, which focuses on personalized branding through URL customization.