Racism is generally understood as either belief that different racial groups are characterized by intrinsic characteristics or abilities and that some such groups are therefore naturally superior to others or as practices that discriminate against members of particular racial groups, for example by perpetuating unequal access to resources between groups.

The definition of racism is controversial both because there is little scholarly agreement about what the word "race" means, and because there is also little agreement about what does and doesn't constitute discrimination. Some definitions would have it that any assumption that a person's behavior would be influenced by their racial categorization is racist, regardless of how seemingly benign such assumptions might be. Other definitions would only include conscious malignant forms of discrimination. Among the questions about how to define racism are the question of whether to include forms of discrimination that are unintentional, such as making assumptions about preferences or abilities of others based on racial stereotypes, whether to include institutionalized forms of discrimination such as the circulation of racial stereotypes through the media and whether to include the socio-political dynamics of social stratification that sometimes have a racial component.

"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 the United Nations conventions, there is no distinction between the terms racial discrimination and ethnicity discrimination.

In politics, racism is commonly located on the far right due to the far right’s common association with nativism, racism, and xenophobia. In history, racism has been a major part of the political and ideological underpinning of genocides such as the holocaust, but also in colonial contexts such as the rubber booms in South America and the Congo, and in the European conquest of the Americas and colonization of Africa, Asia and Australia. It was also a driving force behind the transatlantic slave trade, and behind states based on racial segregation such as the USA in the 19th and early twentieth centuries and South Africa under apartheid. Practices and ideologies of racism are universally condemned by the United Nations in the Declaration of Human Rights.