This is an understated film - which was probably the only way to go, when the subject is so overwhelming that all but the simplest words were lower to fail it. Prejudice comes from the word pre-judge. We prejudge when we have an opinion about a person because of his or her membership in a particular group. It attaches value to those differences in ways that benefit one group at the expense of the other. It is generalized to all members of the group.
Discrimination occurs when prejudices are translated into action.