The Azure AD mobility settings allow you, as an IT administrator, the ability to help ensure users are accessing company data and assets in a secure and compliant way, which you specify through configuring MDM integration within Azure AD. If your users are using personal or managed devices to access corporate data and apps, you'll want to configure MDM with Azure AD.
Configuring MDM integration with Azure AD
Registered versus joined devices
Azure AD registered devices are typically the personal devices in a BYOD scenario on which a user enters their work or school credentials to access their organization resources and data from an organization's domain. The previously mentioned Android and iOS enrollments would be...