Street Fashion is a type of fashion that is personal to you. It is something that displays your personality but it still highly trendy and cool. It may even be seen as controversial to others.
Street Fashion can be just your own clothes that you have either customised or demolished (if you so wish). I.E. The Harajuku Girls have a street fashion: Japanese Anime is their fashion and they dress like that to a) display their personality and b) show their love for Japanimation and Manga.