1. Noun. the ''d''-dimensional Hausdorff content of ''S'' is defined by C_H^d(S):=\lim_{\sup_i r_i \rightarrow 0} \inf\Bigl\{\sum_i r_i^d:\text{ there is a cover of } S\text{ by balls with radii }r_i>0\Bigr\}. ¹
¹ Source: wiktionary.com