I guess we can start here:
Racism is a product of the complex interaction in a given society of a race-based worldview with prejudice, stereotyping, and discrimination. 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. The ideology underlying racist practices often includes the idea that humans can be subdivided into distinct groups that are different in their social behavior and innate capacities and that can be ranked as inferior or superior.[1] Racist ideology can become manifest in many aspects of social life. Associated social actions may include xenophobia, otherness, segregation, hierarchical ranking, supremacism, and related social phenomena.
While 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. According to a United Nations convention, 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.[2]
Today, the use of the term “racism” does not easily fall under a single definition.[3] It is usually found in, but usage is not limited to, law, the social and behavioral sciences, humanities, and popular culture.