The Common Data Service for Apps is the heart of the Microsoft Power Platform. CDS is a secure database hosted in Azure Cloud, with a standard set of entities and record types.
These record types – e.g. accounts, contacts, and different activity types – are expandable, so you can add additional data fields.
Developers can also add new entities to meet their business requirements. Entities are connected to each other and business rules can be created to make fields mandatory, hide them, or set default values.