Dr. Richard Gardner defines PAS - Parental alienation syndrome:

"The parental alienation syndrome (PAS) is a disorder that arises primarily in the context of child-custody disputes. Its primary manifestation is the child's campaign of denigration against a parent, a campaign that has no justification. It results from the combination of a programming (brainwashing) parent's indoctrinations and the child's own contributions to the vilification of the target parent."

For more information go to http://www.paskids.com/ (less info)