Wikipedia®, the on-line free enclyclopedia, defines parental alienation as any behavior by a parent, a child's mother or father, whether conscious or unconscious, that could create alienation in the relationship between a child and the other parent. Parental alienation can be mild and temporary or extreme and ongoing. Most researchers believe that any alienation of a child against (the child's) other parent is harmful to the child and to the target parent. Extreme, obsessive, and ongoing parental alienation can cause terrible psychological damage to children extending well into adulthood. Parental Alienation focuses on the alienating parents behavior as opposed to the alienated parent's and alienated children's conditions.

This definition is different from "Parental Alienation Syndrome" as originally coined by Dr.Richard Gardner in 1987: "a disturbance in which children are preoccupied with deprecation and criticism of a parent-denigration that is unjustified and/or exaggerated." Parental Alienation Syndrome symptoms describe the child's behaviours and attitude towards the targeted parent after the child has been effectively programmed and severely alienated from the targeted parent. Parental alienation, on the other hand, describes the alienating parent's or parents' conduct which induces parental alienation syndrome in children.

Parental alienation is a form of relational aggression by one parent against the other parent using their common children. The process can become cyclic with each parent attempting to alienate the children from the other. There is potential for a negative feedback loop and escalation. At other times an affected parent may withdraw leaving the children to the alienating parent. Children so alienated often suffer effects similar to those studied in the psychology of torture (Sources: External link articles below and late adulthood consciousness of parental alienation). 

Alienating parents often use grandparents, aunts/uncles, and other elders to alienate their children against the target parent. In some cases, mental health professionals become unwitting allies in these alienation attempts by backing unfounded allegations of neglect, abuse or mental disease. Courts also often side with the alienating parent against the target parent in legal judgements because parental alienation is so difficult to detect.

Extreme forms of parental alienation include obsessive brainwashing, character assassination, and the false inducement of fear, shame, and rage in children against the target parent. Moderate forms of parental alienation include loss of self control, flareups of anger, and unconscious alliances with the children against the target parent. In its mildest forms, parental alienation includes occasional mild denigration alternating with a focus on encouraging the children's relationship with the other parent.

Parental alienation often forces children to choose sides and become allies against the other parent. Children caught in the middle of such conflicts suffer severe losses of love, respect and peace during their formative years. They also often lose their alienated parent forever. These consequences and a host of others cause terrible traumas to children as studied in Parental Alienation Syndrome.

Parents so alienated often suffer heartbreaking loss of their children through no fault of their own. In addition, they often face false accusations from their alienated children that they cannot counter with the facts. Finally, they often find themselves powerless to show that this little-known form of cruel, covert, and cunning aggression is occurring or has occurred¹.

¹  Wikipedia GNU Free Documentation License