Street art?

What the fuck defines street art? I always end up in never ending discussions about "street art" and tags/graffiti.
Are tags street art? Definetly not in my opinion but I prefer to see tags in the city cause that gives a feeling that the city is alive. Yeah I know it sounds corny and shit but you get me. Alot of people say that they like that street art phenoma but really don´t like tags. what´s the difference? And yeah I don´t the illegal aspect of it and blah blah blah... For me as long as shit gets reactions it´s good even if it negative. And whats up with these poster/sticker guys that post their shit over peoples tags.
No fucking respect so no respect is what you get back.
There´s not alot o street art or taggers that impress me with their stuff but today i saw some funny shit about Eu.
It said: " Eu slutar här" . "Eu ends here"
So I give that street art shit a chance cause it´s better to make a mark than not doing.
Serious.