From Hindupedia, the Hindu Encyclopedia
By Swami Harshananda
Nirvikalpaka literally means ‘without distinctions’.
Samādhi or total absorption in Brahman is of two kinds:
Vikalpa means distinctions, the consciousness of the many like ‘me’ and ‘Brahman’ and the world. In the savikalpaka samādhi the consciousness of one’s own personality as distinct from Brahman, however attenuated it may be. In the nirvikalpaka state all the awareness of multiplicity including that of oneself as distinct from Brahman, is completely dissolved.
- The Concise Encyclopedia of Hinduism, Swami Harshananda, Ram Krishna Math, Bangalore