This is an exert from the article Why There’s No Such Thing as Reverse Racism. It is a fantastic article and I encourage you to read it in it’s entirety. For now, I want to highlight the explanation/definition of three specific words.
Prejudice is an irrational feeling of dislike for a person or group of persons, usually based on stereotype. Virtually everyone feels some sort of prejudice, whether it’s for an ethnic group, or for a religious group, or for a type of person like blondes or fat people or tall people. The important thing is they just don’t like them — in short, prejudice is a feeling, a belief. You can be prejudiced, but still be a fair person if you’re careful not to act on your irrational dislike.
Discrimination takes place the moment a person acts on prejudice. This describes those moments when one individual decides not to give another individual a job because of, say, their race or their religious orientation. Or even because of their looks (there’s a lot of hiring discrimination against “unattractive” women, for example). You can discriminate, individually, against any person or group, if you’re in a position of power over the person you want to discriminate against. White people can discriminate against black people, and black people can discriminate against white people if, for example, one is the interviewer and the other is the person being interviewed.
Racism, however, describes patterns of discrimination that are institutionalized as “normal” throughout an entire culture. It’s based on an ideological belief that one “race” is somehow better than another “race”. It’s not one person discriminating at this point, but a whole population operating in a social structure that actually makes it difficult for a person not to discriminate.