Once upon at time the answer was fairly simple. It was defined as an irrational hatred of somebody, or a feeling of superiority over someone based purely on their racial origin.
These days, like so many other 'isms and 'obes the definition seems to have been extended to a degree where even mentioning a persons racial origin as a statement of fact can be declared racist.
A persons race is a matter of fact. Like their hair colour, sex or height it is one of the first things you notice about a person. You can't help it, it stands out as one of their major characteristics.
Has the definition of racism gone beyond all bounds? The recent kerfuffle because his ex-caddy referred to Tiger Woods as a Black B*st*rd is a typical case in point. Which is more insulting, the adjective or the noun? As Woods is Afro-American the adjective can be considered bad taste but accurate, the real insult the noun?
In my life I have been called a "young B*", a "long haired B*", a "four eyed B*" and a "White B*". Now as I approach my dotage I get called an "old B*" and a "bald B*".
In all case there was no way I could or can dispute the adjective so take no offence at it, but I have taken great offence at being called a "B*"
The other thing that annoys me is that "Racism" is seen to be a characteristic purely of those with an Anglo-Saxon background and all whites are automatically assumed to be psychotically racist, funnily enough, mostly by other whites.
Isn't this assumption itself racist?
There are many non-white ethnic groups who hate other ethnic groups, including whites, purely on the basis of their skin colour or the part of the world they or their parents came from, yet one never hears them decried as racist.
Is this because to call these groups racist would itself be seen as Racism?
As I said above a persons racial background is a highly visible thing and many people are proud of their origin. The idea is, not to pretend that there aren't different races but to emphasise the fact that a persons origin, like their hair, height or eye colour is an irrelevant factor when judging them.