Individual thoughts, actions, and institutional patterns and policies that create unequal access to power, resources, and opportunites based on imagined differences among groups.
Example
Racism has lead to horrendous crimes in history. Believing that one race is inferior to another has lead to the genocide of Native Americans, Africans throughout the Trans Atlantic slave trade, hate crimes, etc. Even today racism still exists, as institutional racism is a big issue in society. Institutional racism has lead to movements like Black Lives Matter(BLM) to fight injustice in the black community.