Define blackwhite. Why is its definition important to the Party’s survival?

Blackwhite is an important definition for the survival of the Party because it is necessary to change the way one sees things depending on the needs/wants of the party. It can be used in a negative fashion when applied to one's opponent; then saying someone claims that black is white is a negative trait. However, as a member of the Party, when one says black is white and the Party demands such loyalty, then one is "parroting" what a person wants. The other important part of saying that black is white relates to the fact that it can relate to the Party's need to change the truth from day to day, thus emphasizing how their "truth" is forever changing and one must, in order to survive, "forget."