I drive mostly Asian cars which mostly have an air-conditioning interface consisting of a button saying "A/C". This makes sense to me since it's short for "Air Conditioning" (assumption :)). Also the usage is pretty straight forward: you push the button and you gain cold air, release the button and it stops.
However, lately I was driving with my friend's German Car (Audi) and the a-c interface completely confused me. I didn't even find it until my friend helped me out. Apparently you have to deactivate (!) a button saying "ECON". So it's on (a small orange LED indicates "ON") and you have to deactivate (the small orange LED turns off) it in order to activate the air-conditioning.
What does ECON mean? How does this whole concept make sense? Why is it preferable above a common "activate the AC"-button?