What does the notation $|B(x,\epsilon)|$ mean? Is it the volume of the open ball? I saw it from the following:
...It follows from the Lebesgue theory that for almost every $x\in\Omega$, $\lim_{\epsilon\to 0} \frac{1}{|B(x,\epsilon)|} \int_{B(x,\epsilon)} f(x) dx$ exists...
