Hi partner,
Welcome to Dynamics 365 community. :)
Normally, Sales, Commerce, Marketing and other applications are all applications in D365.
First of all, D365 contains 2 type of applications.
One is D365 CRM, complete name is Customer Relationship Management, and it contains many applications like Sales, Customer Service, Marketing, Field Service and many other applications.
The other one is D365 Finical and Operations, provide ERP functionally. F&O also contains Commerce, Human Resource and other applications.
You could get more information by the following links.
https://dynamics.microsoft.com/en-us/
And you could get details for each application.
Best Regards,
Leo
