Get value of q for conditionals

What I'd like to do is to change the location of the left sidebar depending on whether you are in the admin area of the site or not, for that I wonder if I can use the value of Q ($_GET['q']).

I've been told to about the sections.module but I'd rather use flexinodes if possible and still have enough control to assign the location of this menu depending on what part of the site you are on.

Secondly, is it correct to call the Q value the taxonomy path? What are the different elements in the taxonomy? What is the difference between a node and a page when it comes to addressing them in this "content space" or "content hierarchy"?

I am a bit confused...