What is "avyakta"

Avyakta, meaning "not manifest", "devoid of form" etc., is the word ordinarily used to denote Prakrti on account of subtleness of its nature and is also used to denote Brahman who is the subtlest of all and who by virtue of that subtlety is the ultimate support ( asraya) of Prakrti. Avyakta as a category along with Mahat (Cosmic Intelligence) and Purusa plays an important role in the later Samkhya philosophy even though the Bhagavad Gita III.42 retaining the psychological categories altogether drops out the Mahat and the Avyakta (Unmanifest), the two objective categories.