Oneness is the experience of being whole with the Universe, feeling connected with everything in existence at every level. At times it is referred to as unity, Christ Consciousness, or enlightenment.
What is Oneness with God?
There is one energy, and that energy is God, and everything is a unique expression of God. Oneness is a state of being at One with Source, where there is no separation between the Self and Source (God) energy. Oneness is a state of re-membering with Source Consciousness, the Higher Self.