The straight definition of race from Merriam-Webster is:
1: a breeding stock of animals
2 a : a family, tribe, people, or nation belonging to the same stock b : a class or kind of people unified by shared interests, habits, or characteristics
3 a : an actually or potentially interbreeding group within a species; also : a taxonomic category (as a subspecies) representing such a group b : breed c : a category of humankind that shares certain distinctive physical traits
But the more complex question is: where did the concept of race come from?
What Merriam-Webster does NOT tell you is that race in the United States has its roots in history, when Western Europeans arrived in North America. Over the years, it has become socialized and legalized - so that the color of one's skin DOES impact their lived experience.
As I tried to address this question in a couple of blog posts, I realized that I would not be able to do so...or at least not as eloquently as other researchers have done before me. So, in great humility and acknowledgment of researchers I admire, I DO want to point you to a fabulous website and movie about the history of race (follow the previous link). It is an excerpt from the "RACE: Are We So Different" exhibit. I would encourage you to see when this amazing exhibit is in your neighborhood. You will never look at race in the same way again!