Racism is discrimination and prejudice towards people based on their race or ethnicity. Today, the use of the term "racism" does not easily fall under a single definition.
The ideology underlying racist practices often includes the idea that humans can be subdivided into distinct groups that are different in their social behaviour and innate capacities and that can be ranked as inferior or superior.
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 behaviour). 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, and there is no justification for racial discrimination, anywhere, in theory or in practice.
Racist ideology can become manifest in many aspects of social life. Racism can be present in social actions, practices, or political systems (e.g., apartheid) that support the expression of prejudice or aversion in discriminatory practices.
Associated social actions may include nativism, xenophobia, otherness, segregation, hierarchical ranking, supremacism, and related social phenomena.