Hi Rakesh0902,
1. what we need to call Dynamic 365. it is a platform ? it is a application ?
Dynamics 365 is a product line of enterprise resource planning (ERP) and customer relationship management (CRM) applications.
It can be defined differently in different ways. Functionally we can define Dynamics 365 as a ERP & CRM package. In a technical term we can define Dynamics 365 as a Microsoft.NET Web application.
You could refer to this article to understand the definition of Dynamic 365: https://community.dynamics.com/365/b/softchiefmicrosoftdynamics365/archive/2017/07/28/dynamics-365-begineers-guide
2. what will be the application ? What will be the "System/ Core-app" ? What is Module ?
As the picture shows, these are 11 OOB applications in D365, also the System/ Core-app. At the same time, they are also modules in D365. (In actual use, the applications that users can use are based on the licenses they own.)
These applications can be seen as the entry point for users to enter D365.
In addition to these OOB applications, we could also create custom Apps. (Custom entities are not considered System/ Core-app and Module.)
3. what will be the Suite in Dynamics 365?
A suite can be seen as a collection of functional solutions. We can get and import solutions to extend the capabilities of D365.
Please refer to this article for solutions: https://docs.microsoft.com/en-us/dynamics365/customer-engagement/developer/introduction-solutions
4. What is Entity ?
The entities are used to model and manage business data in Dynamics 365.
Conceptually, an entity is like a database table, and the entity attributes correspond to the table columns. Creating an entity record (or, simply a record) in Dynamics 365 for Customer Engagement apps is like adding a row in a database table. The entities are divided into three categories: system, business, and custom.
Please refer to these two articles for details on entities: https://docs.microsoft.com/en-us/dynamics365/customer-engagement/developer/introduction-entities
https://community.dynamics.com/crm/b/xrm/archive/2013/06/20/what-is-an-entity-in-microsoft-dynamics-crm
5. what is office 365?
Office 365 is a collection of online services designed to work together to provide enterprise-grade, anywhere access to email, file sharing, and online meetings. Office 365 includes features that allow administrators to add users, manage passwords and licenses, and much more. Dynamics 365 for Customer Engagement apps takes advantage of the Office 365 administration features to simplify user management. Customer Engagement apps users are created and managed in the Microsoft 365 admin center.
Please refer to this article for Office 365: https://docs.microsoft.com/en-us/dynamics365/customer-engagement/admin/what-office-365-how-does-relate
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Hope this helps.
Best Regards,
Lu Hao