Microsoft's Common Data Service has become a foundational component of many Dynamics 365 applications and a large portion of Power Apps, serving as the database and data management layer with a shared data model, customization capabilities, security, file management, and more.  

Developers work with CDS to model business data, develop user interfaces, build integrations, and automate processes. And while that work continues uninterrupted the work has changed with new terminology that Microsoft has rolled out to describe some of the core elements of the platform.