Triangulation is a situation in which one family member will not communicate directly with another family member, but will communicate with a third family member, which can lead to the third family member becoming part of the triangle. The concept originated in the study of dysfunctional family systems, but can describe behaviors in other systems as well, including work.
Triangulation can also be a form of “splitting” in which one person plays the third family member against one that he or she is upset about. This is playing the two people against each other, but usually the person doing the splitting will also engage in character assassination, only with both parties.
https://en.wikipedia.org/wiki/Triangulation_%28psychology%29#The_Perverse_Triangle
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