(literally, That-ness): That which is the essence of each stage of manifestation. The process of creation, according to Kashmir Shaivism, contains thirty-six stages or steps.

The true or first principle, an element or primary substance. The real nature of the human soul or the material world and the Supreme Universal Spirit pervading the universe.

"thatness", a fundamental cosmic principle.

Elements; faculty.

fundamental truth or principle.

Essence; principle.

("thatness"): a fact or reality; a particular category of existence such as the ahamkara, buddhi, manas; the ultimate Reality (see also atman, brahman)

Tattva is a Sanskrit word meaning 'thatness', 'principle', 'reality' or 'truth'. "tattva - of the truth" from http://vedabase.net/bg/2/16/en1 BG 2.16 According to various Indian schools of philosophy, a tattva is an element or aspect of reality conceived as an aspect of deity. Although the number of tattvas varies depending on the philosopical school, together they are thought to form the basis of all our experience. The Samkhya philosophy uses a system of 25 tattvas, while Shaivism recognises 36 tattvas.