Abhava2

According to Sankaracharya: "Those who say that there is such a thing as Abhava on earth, are neither Srotis (those who understand the Srutis), knowers of Sastras, knowers of Truth, nor Sadhus. Listen! both Bhava and Abhava (existence and nonexistence) are also Brahma" (Maha-avakyadarpanam, vv. 129-30). Thus Brahman is essentially the source or foundation of all that is: both becoming or being, and nonbecoming or nonbeing; and because bhava and abhava exist in the universe, both are Brahman.
A more subtle, deeply philosophical concept is the application of abhava to the unmanifest -- that state of the cosmic essence before "becoming" began its work of differentiation into hierarchical orders, thus bringing about bhava. See also ASAT ; BHAVA ; Sat