Our inner, divine Source, also called the Innermost or Monad, which is not easily definable in conceptual terms. The use of the term "Being" is important though, in relation to its roots:
From the Online Etymology Dictionary: "O.E. beon, beom, bion "be, exist, come to be, become," from P.Gmc. *beo-, *beu-. This "b-root" is from PIE base *bheu-, *bhu- "grow, come into being, become," and in addition to the words in English it yielded German present first and second person sing. (bin, bist, from O.H.G. bim "I am," bist "thou art"), L. perf. tenses of esse (fui "I was," etc.), O.C.S. byti "be," Gk. phu- "become," O.Ir. bi'u "I am," Lith. bu'ti "to be," Rus. byt' "to be," etc. It also is behind Skt. bhavah "becoming," bhavati "becomes, happens," bhumih "earth, world."
"The conception we have of the Being is not the Being. Any intellectual concept we have created about the Being is not the Being. Our opinion of the Being is not the Being. The Being is the Being, and the reason for the Being to be is to be itself." —Samael Aun Weor, The Secret Doctrine of Anahuac