Difference between ManyToOneRel and ForeignKey?
Django relations model exposes (and documents) only OneToOneField, ForeignKey and ManyToManyField, which corresponds to the inner

OneToOneField -> OneToOneRel
ForeignKey -> ManyToOneRel
ManyToManyField -> ManyToManyRel

See source of django.db.models.fields.related for further details.
In django, what's the difference between a ManyToOneRel and a ForeignKey field?