The [Heisenberg's uncertainty principle](http://en.wikipedia.org/wiki/Uncertainty_principle) states the following:

$$\Delta p \cdot \Delta x \ge \frac{h}{4\pi}.$$

While studying for my high school physics exams, I fooled myself into believing that I understood the [uncertainty principle](http://simple.wikipedia.org/wiki/Heisenberg%27s_uncertainty_principle) (at least the implications). But suddenly the question that's nagging me is the following. If the uncertainty $\Delta x$ of an electron is 1.2 nm, does it imply that the probability that the x-coordinate lies within a 1.2 nm range, equal to 100%? Or does it mean that the probability is 95%? Or does it mean something totally different?

I wonder why no author made it clear in the high school/junior college level textbooks. I am uncertain about what uncertainty means.