Application Window: The windows in which the computer is programmed to use various tasks (such as MS Word, MS Excel, Paint, etc.), are called application windows. Most of the work is done with these windows and hence they are called main windows or parent windows.
Document Window: There are some windows that can be used to work with documents. These are called document windows. E.g., MS Word. If an application window has a window-shaped part (usually white) where keyboards can be used to work with documents, those windows are now called document windows. Note the picture number 3.12. One of its practical features is that it is possible to work with different documents in different document windows. When working with a document window, it is possible to minimize it and open another window with the same name on the computer screen.
Modal Window: Windows that cannot be resized, that is, windows that cannot be resized or enlarged, are called modal windows. For example - desktop.
Non Modal Window: The windows that can be resized, that is, the windows that can be made smaller or larger, are called non modal windows. Such as My Documents, My Computer, MS Word etc.
Very useful article