Text files are files that contain simple text data. Text files are created in Windows by the Notepad application, Gedit on Ubuntu, and TextEdit on Mac OS X. There are many other programs called text editors that can create and modify text files. IDLE’s own file editor is a text editor.
The difference between text editors and word processors (like Microsoft Word, or OpenOffice Writer, or iWork Pages) is that text editors have text only. You can’t set the font, size, or color of the text. (IDLE automatically sets the color of the text based on what kind of Python code it is, but you can’t change this yourself, so it is still a text editor.) The difference between text and binary files isn’t important for this game program, but you can read about it at http://invpy.com/textbinary. All you need to know is the this chapter and the Star Pusher program only deal with text files.