This term is used by the Cassiopaea and Ra channeled sources to denote their 'native' state of being. Also the inspiration for the Bringers of the Dawn book is according to these same sources from 6th density. Most crop circles are, according to the Cassiopaeans, produced by entities of 6th density. Many so called wanderers are souls whose home density is the sixth but who have taken incarnation in human form for a specific mission.
We cannot say much that is concrete or verifiable about this subject. Still, since the subject of sixth density relates to much of the inspiration of the present work, we must attempt to place this in some context. The archangels or solar world of the Gurdjieffian cosmology may refer to sixth density. The dhyanic beings or solar beings of Steiner's cosmology may refer to sixth density. The Absolute II of Mouravieff, i.e. the world of all stars and the Christ may be in some relation to sixth density. The comparisons are tentative and we can hardly produce contradiction free or definite descriptions of this level.
The sixth density or 6D is a level of non-material existence where souls have outgrown the need to incarnate in any density. Souls of 1st through 4th densities go through incarnations, with a contemplation period as non-material forms in fifth density in between. 6D is the last stage before union with the One, or seventh density. Seventh density would correspond to the one source of all creation, God the Father of Mouravieff or the Sun Absolute of Gurdjieff.
As with 4D, there is still a concept of individual entities forming social memory complexes, i.e. communities where entities all share the same database of experience and understandings. The esoteric level of human development where understandings are unified through practice of objectivity and where integrity does not allow mismatch of action and understanding would be a precursor of the social memory complex of 4-6D.
Entities of this level are of a service to others orientation as a result of natural factors. This is complex and an exact understanding of this may not be possible at our level. The point is that the idea of service to self is represented in 6D as a concept but not as whole entities. There is still a difference between concept and actuality from the 6D viewpoint. The thought and reality become only non-differentiated in 7D but this is even farther past our capacity of description. Pure service to self does not occur as functioning entities past 4D apparently because the inherent bias for materiality and subjectivity prevents it. A very far advanced STS entity acquires a sort of spiritual mass that causes it to fold up on itself, a bit like a black hole in the material world. If the entity let go of its defining preoccupation with control, it could become objective but then it would no longer be an STS entity.
A 6D entity lives in a world of pure thought or light and is a light form without a fixed body. The Cassiopaeans once said that if two entities could access absolutely all there is, these would in fact be one, indistinguishable from each other. In this sense we could say that all is one from the 6D viewpoint, yet there still is the idea of entity. We see that the idea of objectivity is inherently linked to such a notion of living in unity of omnipresence. An entity that would only see what it wants to see would sort of collapse on itself in such a state and in fact share nothing, except its illusion with itself, which may be the reason why there is no operative STS at that level. To be one with all, one cannot be prejudiced. Again, not being prejudiced does not mean that one cannot assign values to things or choose what one participates in, quite the contrary. We could even say that objectivity and lack of prejudice are prerequisites of metaphysical free will. One cannot choose unless one knows. One cannot know in this sense if one thinks wishfully.
We can say very little about perception of time or space of 6D. We could infer that events of the physical densities appear as from a bird's eye perspective, with different possible pasts and futures alongside each other, as a sort of tangle of threads of different probabilities. In the terms of Gurdjieffian cosmology, we could say that the 6D entity sees at least the dimensions of linear time and eternity, seeing the plane containing all possible timelines as from a height in a third dimension. The word eternity in the 4th Way sense refers to a dimension perpendicular to linear time, as in the set of all possible timelines. In a sense we could say that the experience of 6th density involves six dimensions. Again, these are approximate visualizations. Generally, the 6D sources speak as if the past of 3D were an open book and the future a branching tangle of probabilities.
In this sense it is sometimes said that time does not exist in the higher densities. This should not be taken too literally. Rather this seems to mean that time does not appear as a one-way street with most things hidden behind a corner, as it mostly does to us.
The Cassiopaeans repeatedly use the term you in the future' when speaking of themselves. This can be understood as referring to at least one possible future where Laura Knight-Jadczyk, the channel, and maybe some fellow travelers have become the C's. However, there can be futures where this is not the case as well as possible pasts where no such channeling took place to begin with. The process of contact then is a link pulling certain lines of past towards certain lines of futures. The 6D experience may be akin to guiding this from a bird's eye view. Still, in a sense, the Cassiopaeans are creating themselves by guiding their 'past' selves. Yet all such metaphors are incomplete because their very language assumes linear causality which most likely does not apply in the 6D perspective.
To complete this summary, we will quote Ra:
Ra: 'In relationship to the densities, the sun body may physically, as you would say, be seen to be a large body of gaseous elements undergoing the processes of fusion and radiating heat and light. Metaphysically, the sun achieves a meaning to fourth through seventh density according to the growing abilities of entities in these densities to grasp the living creation and coentity, or other-self, nature of this sun body. Thus by the sixth density the sun may be visited and inhabited by those dwelling in time/ space and may even be partially created from moment to moment by the processes of sixth density entities in their evolution. [...] In this density some entities whose means of reproduction is fusion may choose to perform this portion of experience as part of the beingness of the sun body. Thus you may think of portions of the light that you receive as offspring of the generative expression of sixth-density love.'