What is the Mail Merge process?

Answer: About the mail merge process and merge fields

Explanation:
A mail merge is the process of generating form letters and other Microsoft Word documents
that are personalized for the recipient, who is often a contact or lead. The content of each
document is predefined in a mail merge template. Mail merge templates include variables
called merge fields where data from your Salesforce records — for example a contact’s
name and address—displays in the generated document.