I was reading the paper "The Pin Groups in Physics: C, P, and T" by M. Berg, C. Morette-DeWitt et al. in which they analyze the (double) covering groups of (Lorentzian) orthogonal groups $\operatorname{O}(s, t)$, the so-called $\mathrm{Pin}$-groups.
In one of the sections they quickly cover the (standard) definition of $\textbf{pinors}$ as sections of a vector bundle associated to a $\mathrm{Pin}$-bundle. As this paper is linked to quantum field theory, they consider both massless and massive pinor fields and define them as sections of vector bundels associated to $\mathrm{Pin}$-bundles reducible to a $\mathrm{Spin}$-bundle and $\mathrm{Pin}$-bundles that do no admit such a reduction, respectively.
On the other hand, they define a $\textbf{spinor}$ field as a section of a vector bundle associated to a $\mathrm{Spin}$-bundle.
What exactly is the difference between a massless pinor and a spinor? Lies the difference in the fact that a $\mathrm{Spin}$-bundle is not simply a $\mathrm{Pin}$-bundle admitting a $\mathrm{Spin}$-reduction, but actually a specific choice of reduction?