What is the essential difference between win8 application and traditional desktop program?

How to put it? win8 is like a combination of a window system and a win8 tablet system (win8RT is saface lithography), so he can use both traditional windows programs and win8 tablet applications, while win8RT system can only use tablet win8 applications. The purpose of the two sets is to replace the original windows system, make win8 more humanized, keep pace with the times, and form a competitive and complementary relationship with the current phablet (wp8 system). I wonder if you are satisfied with my personal introduction.