A pre-judgment or unjustifiable, and usually negative, attitude of one type of individual or groups toward another group and its members. Such negative attitudes are typically based on unsupported generalizations (or stereotypes) that deny the right of individual members of certain groups to be recognized and treated as individuals with individual characteristics.
Definition: Prejudice
Prejudice
A very simple defintion that I use with children is to pre-judge.
Here's a more technical definition provided by the Institute for Democratic Renewal and Project Change Anti-Racism Initiative: