Racism is the belief in the superiority of one race over another. It may also mean prejudice, discrimination, or antagonism directed against other people because they are of a different race or ethnicity. 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.
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 both 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). Therefore, 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. According to a United Nations convention on racial discrimination, there is no distinction between the terms "racial" and "ethnic" discrimination. The UN convention further concludes that superiority based on racial differentiation is scientifically false, morally condemnable, socially unjust and dangerous. It also declared that there is no justification for racial discrimination, anywhere, in theory or in practice.
Historically, racism was a major driving force behind the Atlantic slave trade. It was also a major force behind racial segregation especially in the United States in the nineteenth and early twentieth centuries and South Africa under apartheid; 19th and 20th century racism in Western culture is particularly well documented and constitutes a reference point in studies and discourses about racism. Racism has played a role in genocides such as the Holocaust, and the Armenian genocide, and colonial projects like the European colonization of the Americas, Africa, and Asia. Indigenous peoples have been –and are– often subject to racist attitudes.