Mail merge is a feature in word processing applications that allows users to send a similar letter or document to multiple recipients with personalized information. It is a tool for writing a personalized email or letter to many people simultaneously, and it imports data from other sources like worksheets and uses it to replace placeholders throughout the message with the relevant information for each individual that is being texted. In other words, it is the automatic addition of names and addresses from a database to letters and envelopes.

To perform a mail merge, you need to follow these steps:

1. Prepare data of names and addresses in Excel data sheet for mail merge.
2. In a new blank word document, start mail merge.
3. Insert a merge field.
4. Preview and finish the mail merge.
5. Save your mail merge.

Mail merge is a useful tool that will allow you to easily produce multiple letters, labels, envelopes, nametags, and more using information stored in a list, database, or spreadsheet. It is a handy feature that incorporates data from both Microsoft Word and Microsoft Excel and allows you to create multiple documents at once.