What does kppa stand for?

The source code of automatic_density function and automatic_desity_by_vol function of class Kpoints were confusing for me.
What does argument “kppa” stand for? If this stands for “kpoints per atom”, I thought line 1221 should be
ngrid = kppa * structure.num_sites
and line 1292 should be
kppa = kppvol * vol / structure.num_sites