It's from the Airl interviews. The book they are publishing soon has the information on it. One of the original aliens recovered during Roswell and was interviewed by a nurse for the military. The alien referred to herself as Airl. Maybe more importantly BEING and IS are terms used heavily in philosophy. A being is essentially a moral agent. Is means the identity property. Either the airl thing is made-up because there's obvious influences from philosophy, or Airl came up with the term IS-BE after reading lots of human literature. In the interview/story Airl spends a week or so speed reading tons of books in order to properly communicate with the nurse.
Renee Descartes' famous quote "I think therefore I am" is essentially him identifying he's an ISBE. He was trying to find a logical basis for scientific theories and all he realized was he can't justice that anything exists except for his own thoughts, and his own thoughts confirm that he exists.
The Airl story is great you should check it out.