What is π charges and bond indices?

With $n_k$ electrons in orbital $k$ (0, 1 or 2) and real coefficients $c_{rk}$, the $\pi$ charge on atom $r$ is $q_r = \sum_k n_kc_{rk}^2$ (the number of $\pi$ electrons it carries), and the $\pi$ bond index of the bond $rs$ is $p_{rs} = \sum_k n_kc_{rk}c_{sk}$.