Azure AD provides you with common identity and access capabilities to all web services. Whether you are using Office 365, Microsoft Azure, Intune, or others, you're already using Azure AD to help turn on sign-on and access management for all these services.
Azure AD paid services like Enterprise Mobility + Security complement other web services like Office 365 and Microsoft Azure with comprehensive enterprise-scale management and security solutions.
Source: https://learn.microsoft.com/en-us/azure/active-directory/fundamentals/active-directory-faq