While you're writing in the box, a Format tab will appear in the top taskbar, which you can use to customize the box's text (font, character size, etc.) independently of the regular document's text.

A Text Box is a feature in Word that focuses on its content and displays essential text such as headings and quotes. 1] How to insert a Built-in Styles Text Box Click the Insert tab on the menu bar.

In Microsoft Word, you can insert built-in or custom fields into your Word document that may change within your document. Learn how to insert a Text field in Word.

Microsoft Word’s content controls make it easier than ever to use dependent controls in your templates to update content all at once.

When inserted this way, the default frame has a border. At this point in Word’s evolution, I can think of no reason to use a frame instead of a text box other than defining the frame via a style.