In existographies, nothingness, literally "no-thing-ness", is a semi-synonym of the terms void, vacuum, or emptiness of space; in Aristotelian terms, a place in which there is nothing; in philosophical terms, a conjectured state into which "being" goes. [1]

Overview

The term "nothingness" tends to arise in philosophical discussions on "being" and "nonbeing" and or existence and non-existence.

Quotes
The following are related quotes:

“Nothingness contains all things; it is more precious than gold, free from birth and destruction, more pleasant than the sight of pure light, more noble than the blood of kings, comparable with the sky and higher than the stars, more powerful than a bolt of lightning, perfect and rich in all its parts.”
— Otto Guericke (1672), The Magdeburg Experiments on the Vacuum of Space (pg. 99); cited by Edward Grant (1981) in Much Ado About Nothing (pg. 216); cited by Helge Kragh (2014) in The Weight of the Vacuum (pg. 6) [1]

“The first task of philosophy, is to conceive of absolute nothingness.”
— Georg Hegel (1802), Faith and Knowledge (Glauben und Wissen) (Ѻ)

References
1. Guericke, Otto. (1663). New Magdeburg Experiments: on the Vacuum of Space (Ottonis de Guericke Experimenta Nova (ut vocantur) Magdeburgica de Vacuo Spatio) (translator and preface: Margaret Ames) (place, pg. 84; gold, pg. 99). Publisher, 1672; Kluwer, 1994; Springer, 2012.

Further reading
● Grant, Edward. (1981). Much Ado about Nothing: Theories of Space and Vacuum from the Middle Ages to the Scientific Revolution (Guericke, 9+ pgs). Cambridge University Press.

External links
● Nothingness – Stanford Encyclopedia of Philosophy.