Dummy if board interlock exists (Adams & Mehran, 2012)
 
We classify boards as being interlocked if any inside director sits on the board of an affiliated or outside director  (Adams & Mehran, 2012)
  
 
Interlocking directorate refers to the practice of members of a corporate board of directors serving on the boards of multiple corporations. A person that sits on multiple boards is known as a multiple director. Wikipedia