I have said before in this and other fora that the best definitions I have come across are stated by Kwame Anthony Appiah in his recent book "In My Father's House" . I think his ideas are significant because of the depth and scope of his knowledge and experience and the fact that he is an internationally recognized scholar. I believe him capable of making his points clearly at any level of discourse. Unfortunately he's not on this particular distribution. So I will paraphrase.

racialism:

The belief that there are differences between human beings which are inherited such that they can be ordered into separate races in such a way that each race shares traits and tendencies which are not shared by members of any other race. Each race has an 'essence'.

All forms of racism build from the premise of racialism. Notice that racialism is not saying anything 'good' or 'bad' about races just that mutually exclusive races absolutely exist and divide the species. The racialist would argue that you could trace the bloodlines of Jews throughout history and that you can definitely determine the 'jewness' of any human being according to his racial 'essence'.

A racialist does not necessarily believe that the races, as we understand them in America are complete. He may say that there are, in actuality, 37 races. We just don't know what they are yet. The racialist's point however is that race, whatever it turns out to be, is deterministic of human behavior and that we need to know.

 

extrinsic racism:

The extrinsic racist says that there is a moral component to the 'essence' of a race which warrants differential treatment. These differences are, to the extrinsic racist, not particularly controversial. The extrinsic racist, while maintaining the belief for example that Jews are greedy, might not feel anything wrong with befriending a Jew. The extrinsic racist might very well applaud the Jew who proves himself not greedy and call him a credit to his race.

 

intrinsic racism:

The intrinsic racist says that the moral 'essence' of a race establishes an incontrovertible status for the race. no matter what an individual member of a race does he should be treated just like the rest of his race. the intrinsic racist would argue that the Jew is so greedy that he would hide his greed in order to gain other's confidence or that this generous person is simply not a Jew.

I use these definitions for a purpose. My interest is in generating and maintaining anti-racist praxis in individuals for the primary purposes of ridding racism from American politics. Thus it is important that these categories work for political ideologies as well as the thoughts of individuals. An individual bigot may be converted for better or worse any day of the week, but a policy enacted by like-minded individuals at any moment in time survives the individual.

Thus whether or not one individually holds racist ideas, the existence of racist policies is that citizen's responsibility.