I have a friend that goes to a college around here. We'd been out on a couple dates and hung out quite abit, made out and some other innoculous things..
Well the question camea couple weeks ago: "what are we?"
Knowing that I don't personaly want anything serious, I kept in mind that she might and didn't discard the possibility of anything serious in the future.
My response:
"Just two people that are looking for good company"
She replied with something else, I don't remeber exactly, but I remember that I replied with something along the line of:
"I like to let things happen on their own". I don't remember exactly what I had said, but I got across the point that I wanted it to stay as friends if I lost the benefits, because her friendship is more important to me than the other things :P.
I was impressed with myself as to how clever it was, and that she took it well. One of her friends thinks we are dating, and often refer to us as so. My friend and I both know different, so we just smile and nod

.
Long and boring story short: If she asks what it is, let her know what you would like out the relationship, emphasize friendship if that's more important to you. All in the ways as to keeping your options open till you find the one that you would like to be serious. Just be careful as to what you say, because I have learned from my limited experince, It will ALL be heard. Connotitions and Literal meanings both.