Kindly check the below link for Sub modules of CRM
https://www.infallibletechie.com/2013/05/sub-modules-of-crm.html


Sales Cloud:

Sales Cloud refers to Sales module in CRM. Sales module include Lead Conversion, Account Management, Opportunity Management, etc.

Service Cloud:

Service Cloud refers to Service module in CRM. Service module includes Case Management, etc.

To know more about Service Cloud, check the following link:

https://www.infallibletechie.com/2017/10/salesforce-service-cloud.html