A holon is a system (or phenomenon) which is an evolving self-organizing dissipative structure, composed of other holons, whose structures exist at a balance point between chaos and order; it is sometimes discussed in the context of self-organizing holarchic open systems (or, SOHO systems).A holon is maintained by the throughput of matter–energy and information–entropy connected to other holons and is simultaneously a whole in and itself at the same time being nested within another holon and so is a part of something much larger than itself. Holons range in size from the smallest subatomic particles and strings, all the way up to the multiverse, comprising many universes. Individual humans, their societies and their cultures are intermediate level holons, created by the interaction of forces working upon us both top-down and bottom-up. On a non-physical level, words, ideas, sounds, emotions—everything that can be identified—is simultaneously part of something, and can be viewed as having parts of its own, similar to sign in regard of semiotics. In 2013 Australian academic JT Velikovsky proposed the holon as the structure of the meme, the unit of culture, synthesizing the major theories on memes of Richard Dawkins, Mihaly Csikszentmihalyi, E. O. Wilson, Frederick Turner and Arthur Koestler. Defined in this way, holons are related to the concept of autopoiesis, especially as it was developed in the application of Stafford Beer to second-order cybernetics and viable system theory, but also Niklas Luhmann in his social systems theory.

Since a holon is embedded in larger wholes, it is influenced by and influences these larger wholes. And since a holon also contains subsystems, or parts, it is similarly influenced by and influences these parts. Information flows bidirectionally between smaller and larger systems as well as rhizomatic contagion. When this bidirectionality of information flow and understanding of role is compromised, for whatever reason, the system begins to break down: wholes no longer recognize their dependence on their subsidiary parts, and parts no longer recognize the organizing authority of the wholes. Cancer may be understood as such a breakdown in the biological realm.

A hierarchy of holons is called a holarchy. The holarchic model can be seen as an attempt to modify and modernise perceptions of natural hierarchy.

Ken Wilber comments that the test of holon hierarchy (e.g. holarchy) is that if all instances of a given type of holon were removed from existence, then all those holons of which they were a part must necessarily cease to exist too. Thus an atom is of a lower standing in the hierarchy than a molecule, because if you removed all molecules, atoms could still exist, whereas if you removed all atoms, molecules, in a strict sense would cease to exist. Wilber's concept is known as the doctrine of the fundamental and the significant. A hydrogen atom is more fundamental than an ant, but an ant is more significant.

The doctrine of the fundamental and the significant is contrasted by the radical rhizome oriented pragmatics of Deleuze and Guattari, and other continental philosophy.

A significant feature of Koestler's concept of holarchy is that it is open ended both in the macrocosmic as well as in the microcosmic dimensions. This aspect of his theory has several important implications. The holarchic system does not begin with strings or end with the multiverse. Those are just the existing limits of the reach of the human mind in the two dimensions at the present time. Those limits will be crossed later on because they do not encompass the whole of reality. Karl Popper (Objective Knowledge, 1972) teaches that what the human mind knows and will ever know of truth at a given point of time and space is verisimilitude - something like truth, and that the human mind will continue to get closer to reality but never reach it. In other words, the human quest for knowledge is an unending journey with innumerable grand sights ahead but with no possibility of reaching the journey's end. The work of modern physicists designed to discover the theory of everything (TOE) is reaching deep into the microcosm under the assumption that the macrocosm is eventually made of the microcosm. This approach falls short on two counts: the first is that the fundamental is not the same as significant and the second is that this approach does not take into account that the microcosmic dimension is open ended. It follows that the search for TOE will discover phenomena more microcosmic than strings or the more comprehensive M theory. It is also the case that many laws of nature that apply to systems relatively low in the hierarchy cease to apply at higher levels. M theory might have predictive power at the sub-atomic level but it will inform but little about reality at higher levels. The work of the particle physicists is indeed laudable but possibly they should give the theory they are looking for another name. This is not to claim that the concept of holarchy is already the theory of everything.