How would you define a short term relationship?

Say a little more than the obvious ie. such as no commitment or they are shorter relationships. How many women would you say are looking for STR's and why are they desired? (and I mean that question in a purely academic kind of way-I'm not saying that women shouldn't want STR's) Say something that gives a general impression of the idea of an STR. Is an STR the same thing as a fling? I imagine there's a distinction.