pure breeding – where does the term come from??

it simply means breeding from same species of male and female.

Purebreds, also called purebreeds or pedigreed/pedigree, are cultivated varieties or cultivars of a species, achieved through the process of selective breeding. When the lineage of a purebred is recorded, that animal is said to be pedigreed. Therefore, although the terms are often used synonymously, there is a difference: all pedigreed animals are purebred, but not all purebred animals are pedigreed.