[Wolfstar]

I thought one of the definitions of a separate species was that two different parent species could not produce fertile offspring.

That's a common, but incorrect, understanding of the term. Merriam-Webster defines the word "species" as follows:

A category of biological classification ranking immediately below the genus or subgenus, comprising related organisms or populations potentially capable of interbreeding, and being designated by a binomial that consists of the name of a genus followed by a Latin or latinized uncapitalized noun or adjective agreeing grammatically with the genus name.

[toast]

Then what is the difference between a separate race and a separate species?