seigen

I have a question about backing up files:
You said that I should not back up any executable files or screensavers. Do all application type files count as .exe files even when they don't have the extension written? To clarify, is a file named "game" without an extension that is categorized as an application file, the same as if it were named "game.exe"? If not, how can I tell that an application file is not an executable file?