Prebuilt email templates are email templates that have been created and provided by Salesforce for common use cases such as sending welcome messages, confirmation emails, etc. They can be used by Cloud Kicks to have consistency when communicating with customers on cases via email channel with categories to help search for the proper message. Prebuilt email templates can be accessed from the email action in the case feed or from the email composer in Lightning Experience. They can also be filtered by category to find the most relevant template for each case. Prebuilt quick texts, prebuilt flow templates, and prebuilt auto-responses are not solutions for having consistency when communicating with customers on cases via email channel; they are used for different purposes such as inserting common phrases, creating guided processes, or sending automated replies. References:
https://help.salesforce.com/s/articleView?id=sf.email_templates_prebuilt.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.email_templates_use.htm&type=5