Fields in Word are used as placeholders for data that might change in a document and for creating form letters and labels in mail-merge documents.
Fields in Word are used as placeholders for data that might change in a document and for creating form letters and labels in mail-merge documents.
Word inserts fields automatically when you use particular commands, such as when you insert a page number, when you insert a document building block such as a cover page, or when you create a table of contents. You can also manually insert fields to automate aspects of your document, such as merging data from a data source or performing calculations.
Source: https://support.office.com/
