1) a term that when used implies that someone has mistakenly and usually hatefully expected something, usually negitive, from a certain other or group of others.
2) Anytime you assume someone will help/hurt you based on all the knowledge availible, usually the knowledge doesn't tell the full story.
1) the prejudice girl clutched her purse when theblack guy walked by.
2) I asked the cop where the nearest drugstore was but he didn't know.
Prejudice often involves creating an opinion of a person based off some quality that doesn't directly correlate to that person's character. For example, homomsexuality doesn't necessarily make a person bad; but for that quality, some people hate.
The condition of believing that one group, most often one the prejudor belongs to, is superior to another group. Most often applies in a negative manner, against those of different race, religion, creed, and nationality. see stereotype, anti-semetism, racism.
Hating people because they're black, gay, Jewish, Muslim, or whatever doesn't make much sense. You can easily find ways to hate people on an individual basis.