According to psychiatrist, Dr. Edward Kruk, parental alienation in divorce involves the "programming" of a child by one parent to denigrate the other "targeted" parent, in an effort to undermine and interfere with the child's relationship with that parent, and is often a sign of a parent's inability to separate from the couple conflict and focus on the needs of the child. Such denigration results in the child's emotional rejection of the targeted parent, and the loss of a capable and loving parent from the life of the child.
These behaviors whether verbal or non-verbal, cause a child to be mentally manipulated or bullied into believing a loving parent is the cause of all their problems, and/or the enemy, to be feared, hated, disrespected and/or avoided.
Twenty years ago, psychiatrist Richard Gardner developed the concept of "parental alienation syndrome", defining it as, "a disorder that arises primarily in the context of child custody disputes. Nevertheless a task force of the American Psychiatric Association has decided not to list the disputed concept of parental alienation in the updated edition of its catalog of mental disorders. The fact that many professionals believe it is indeed a mental disorders is telling.
There is even a Parental Alienation Awareness Day (April 25).
In my practice, and I think in the general public, the term conveys how a child's relationship with one estranged parent can be poisoned by the other parent. This can be done openly, overtly, and aggressively, or subtly, non-verbally, with tone or body language, or even by third parties, relatives or friends of either parent. Many clients are often in denial when confronted with evidence of such behaviors as no parent wants to admit to themselves they may be damaging their children.
Sadly, this is not an uncommon practice in many of the divorce and child custody cases I have worked with over the past nearly 20 years and it appears to be increasing. I say "sadly" because there is ample evidence that a parent who would teach a child to hate or fear the other parent represents a grave and persistent danger to the mental and emotional health of that child. No parent would purposely jeopardize the physical health of their child and certainly should take the same precautions regarding their mental and emotional health.
Finally, from a purely pragmatic perspective regarding child custody and visitation issues, judges I deal with in Williamson and Travis county are typically offended by reports of parental alienation on the part of one parent, and may be influenced to rule in favor of the unfairly alienated parent.
Source: Co-Parenting After Divorce, Rising to the Challenge, Rising to the challenge, Edward Kruk, Ph.D., April, 2013