Race

Races are categories based on physical characteristics. However, race is not a scientific useful category:

"The fact that, given enough genetic data, individuals can be correctly assigned to their populations of origin is compatible with the observation that most human genetic variation is found within populations, not between them. It is also compatible with our finding that, even when the most distinct populations are considered and hundreds of loci are used, individuals are frequently more similar to members of other populations than to members of their own population. Thus, caution should be used when using geographic or genetic ancestry to make inferences about individual phenotypes."

Race however, is relevant to sociology, etc., insofar as it has a measurable effect on the treatment of individuals due to their "race" (that can be either negative or positive, as for example, in the case of white privilege).

Race as a Social Construct

Understanding that Race is not scientifically important (or at least not more important than say, eye color) theorists in Critical Theory, Post-Colonial Studies, and basically every relevant left-wing movement in the last century have advanced the theory that race is a social construct. This means that Race is not an atavistic attitude, but rather an attachment of certain attributes to a certain racial category, in a way that has nothing to do with reality. In this sense, race can be analyzed as an Ideology (i.e., an imagined relation to real conditions of existence, basically, an untrue idea that is implanted through socialization). For example, black people in the U.S. were racialized as slaves, such that to be black meant to be a slave. This of course, is untrue, but it does not matter that race is irrelevant to being a slave inherently, only that people thought this was true (i.e., it is imagined).