My interpretation of it is that a break means that you have 'semi-broken up'. What I mean by that is that youre not really boyfriend and girlfriend anymore but at the same time you shouldnt be seeing other people until the break is officially a break-up, because you both still may get back together. Hard to explain, but thats just my own definition of things.
In reality I found that (as gatorclaws said) a break is really just an easier way of breaking up for the person initiating it.