I am not sure if this question is appropriate for this site, but here it goes. I am not a geometer, so I am not familiar with notation in the area.
I am interested in the moduli space of $r$-spin structures. Let $[C,p_1,...,p_n] ∈ \mathcal{M}_{g,n}$ be a nonsingular curve with distinct marked points. Then some authors define a log-canonical bundle, denoted by $\omega_C(\sum p_i)$ (for example this paper)? What is a log-canonical bundle as opposed to a canonical bundle and what does the data $(\sum_i a_i p_i)$ where $a_i$s are integers meant in this context?