When you add a field that represents information from a data file to the main document, it is always surrounded by chevrons (« »).
Officially, a field is a set of codes that instructs Word to insert information into a document automatically. Informally, you can think of fields as placeholders.
In a mail merge, you'll mostly use fields as placeholders for information that comes directly from a data file. For example, in the letter on the left, fields have been added for information stored in the Address and Name columns of a customer data file.
You can also use fields to insert information that comes from your computer's operating system or results from an action or calculation. You'll learn more about those fields in a later section.