In plain words
In its ripening, the happiness gained in nirvikalpa samādhi is beyond description. It is equal to ‘nectar’. Nirvikalpa means the state free of all intention. That which has no vikalpa is nirvikalpa. It can be attained by sādhana. Nirvikalpa samādhi is of two kinds (according to the Yoga Śāstra and according to Advaita Vedānta). One is “the form of non-dual contemplation”. The second is “the form of the non-dual state”. If there arises a ‘mode of mind taking the form of Brahman’ alone, free of the triad, that is “the form of non-dual contemplation” (according to the Yoga Śāstra). If one is dissolved in the state of one's own nature with attributes, it is “the form of the non-dual state” (according to Advaita Vedānta).