It isn't exactly definable, and therefore it's objective depending on the individual, or culture.
But if you're asking me personally? Well, now...that's another question entirely. There is no set definition with me. Prejudice is a feeling and it can be muted or it can be overt. I've suffered enough from it and in some ways I have problems putting my finger on it too.
I can tell you that it has much to do with being thought of as less than, or weaker than. For example, someone can say to me, "Oh, you're an eloquent speaker!" Which does not sound prejudicial, but it *is* if we're simply discussing normal, every day things. If I were giving a speech as Valedictorian to my senior class I'd be honored. If I were told that by someone in an interview, I'd be incensed.
Prejudice is situational. It's relative to the manner words are spoken, in the context its meant, and to the individual to whom its spoken. Sometimes sheer ignorance can be prejudicial (unintentional prejudice) or sometimes you know it and its overt ("I don't want any blankety-blanks ruinin' mah country with their blankety blank horseshit!").
Context to me is key.
And yep, I'm prepared to discuss this.