O que é Mark-out curve?

The mark-out curve of a set of fills is the quantity-weighted average, as a function of the horizon $h$, of each fill’s mark-out (Book 2, chapter 15), $s_i\,(m(t_i + h) - p_i)$ for a fill of side $s_i$ at price $p_i$ and time $t_i$, against a reference price $m$: the mid, or the microprice (chapter 8).