The Normal.dot file is the file that stores all of your default settings in Microsoft Word.
When in Microsoft Word on a Mac, sometimes the program might spontaneously shutdown. This could be due to a corruption in the normal.dot file.
To solve, you can remove your normal.dot or normal file by deleting it or sending it to the trash. Then, when you re-open word, it will search and not find the normal template. It will then create a new one, eliminating problems that may have been present in the old one.