OK, if we talk about Neandertalers and so on then the term "human races" could make sense. In a hypothetical RPG 50k years ago, the difference between them and humans may be similar to the differences between humans and elves in a fantasy setting.
I think of races in DnD similar to races of dogs in the real world. There are many people who belong clearly to one race, some of them have influences from other races so they look like a member of one race that looks a bit different and there are some people who are such a mix of races that it is hard to put a name on it.
In the end "race" is just a tag you put on a creature in order to define their stats and skills.
Finally my definition of racism:
For me racism means that somebody believes there are several distinct races and some of them are superior to others. Usually the racists believe that they belong to the superior race.
My ultimate example for racism is in Disco Elysium.
A big guy stops you and says "YOUR BODY BETRAYS YOUR DEGENERACY." Then he starts an endless talk why there are over 20 or so distinct human races and why he belongs to the one that is destenied to rule all others. My usual reaction is to punch him in the face.
Prof. Dr. Dr. Mad S. Tist 
