The belief that Romanians are all criminals and Polish steal all our jobs 
Often that's white on white though. I recently heard the term "colourism" which I'd never heard before, but is when blacks discriminate against other blacks that are darker than they are. Lighter = good, darker = bad.
Ultimately it's all bigotry and discrimination. As a PP said, despite the official definition, socially 'racism' is discrimination against black and brown people based on the systematic oppression of white people, so really we need a new word to describe other forms, out of respect of that historic oppression if nothing else.