Association with a group of people based on shared physical traits.
During European colonial expansion in the 17th century, the social construct of race was created (largely around skin color) in order to develop a hierarchy within the human species, with light-skinned people groups representing the highest level of humanity.
For decades Eurocentric cultures attempted to find scientific evidence to back their race theories. While there was certainly no shortage of scientific “proofs” provided to defend racial hierarchies, those findings have now been discredited.
While race isn’t real, in the sense that the concepts of race were built on false assumptions, the effects of race-based ideologies and institutions are very real.
For more background on the creation of the construct of race, watch the excellent documentary series Race: The Power of An Illusion created by California Newsreel. Also, PBS created a helpful online companion/guide to the series.