What is a dialog box?
What dialog boxes are available in Excel?
Dialog boxes are special windows which are used by computer programs or by the operating system to display information to the user, or to get a response if needed. They are so-called because they form a dialog between the computer and the user—either informing the user of something, or requesting input from the user, or both. In GUI terminology, a dialog box is a user control or widget. See more here.
These dialog boxes vary from simple message boxes to complex containers consisting of option buttons, command buttons, tabs, check boxes and more to facilitate interface with the user. The FORMAT CELLS box, the FILE OPEN box, the FILE SAVE box are all examples of dialog boxes in Excel. Excel has more than 100 built-in dialog boxes and if need be you can add your own dialog box.