Racism is the belief that groups of humans possess different behavioral traits corresponding to inherited attributes and can be divided based on the superiority of one race or ethnicity over another. It may also mean prejudice, discrimination, or antagonism directed against other people because they are of a different ethnic background. Modern variants of racism are often based in social perceptions of biological differences between peoples. These views can take the form of social actions, practices or beliefs, or political systems in which different races are ranked as inherently superior or inferior to each other, based on presumed shared inheritable traits, abilities, or qualities. There have been attempts to legitimize racist beliefs through scientific means, such as scientific racism, which have been overwhelmingly shown to be unfounded. In terms of political systems (e.g. apartheid) that support the expression of prejudice or aversion in discriminatory practices or laws, racist ideology may include associated social aspects such as nativism, xenophobia, otherness, segregation, hierarchical ranking, and supremacism.

While the concepts of race and ethnicity are considered to be separate in contemporary social science, the two terms have a long history of equivalence in popular usage and older social science literature. "Ethnicity" is often used in a sense close to one traditionally attributed to "race", the division of human groups based on qualities assumed to be essential or innate to the group (e.g., shared ancestry or shared behavior). Racism and racial discrimination are often used to describe discrimination on an ethnic or cultural basis, independent of whether these differences are described as racial.