Fractal dimension of discrete sets and percolation

There are various notions of dimension in fractal geometry to characterise (random and non-random) subsets of ${\mathbb{R}}^d$. In this expository text, we discuss their analogues for infinite subsets of ${\mathbb{Z}}^d$ and, more generally, for infinite graphs. We then apply these notions to critical percolation clusters, where the various dimensions have different values.