Definition - What does Nirvikalpa mean?
Nirvikalpa is a Sanskrit term derived of two roots; ni meaning without, and vikalpa meaning conception. It can be loosely understood as a kind of awareness without the modifications of the mind, or a state of no-thought.
In the Yoga Sutras of Patanjali, this term is used to describe meditation without an object, which leads to Samadhi. Meditation with support of an object is called Samprajata samadhi.
Yogapedia explains Nirvikalpa
Nirvakalpla Samadhi, is considered to be the highest form of enlightenment, in which awareness is experienced outside of the mind, as one with universal bliss. This meditative state is one without thoughts, conceptions, ideas or form, where true peace can be found.
It is said that that nirvakalpa samadhi is the highest level of samadhi a spiritual master can obtain. If one does reach nirvakalpa samadhi, it can only be held for a few hours or days at most, as it is such a high state of spirituality that it is believed the practitioner's soul could leave their body and pass over to the other side during nirvakalpa samadhi.