A hologram is an image which appears to have depth because its appearance changes according to the angle of observation. We could say that each point in the hologram contains elements of other points, albeit at a lower resolution. The idea is vaguely similar to individual entities being the universe in microcosm, i.e. they contain the broad outline of the containing whole, although it is scaled down and does not contain all the detail and variety.
The idea is somewhat similar to the idea of the universe being fractal-like, i.e. self-similar at all scales. This is to say that the same patterns occur in the extremely small and the extremely large, for example, an atom could be compared to a solar system because both have a nucleus and a variable number of satellites.
The idea of holographic nature is a mental model and not a theory that would make testable predictions. It is a way of looking at things, not a model proposing to allow exact modeling of any real processes. The idea of holographic nature is reminiscent of the hermetic maxim, 'as above, so below.'
In terms of consciousness, the Cassiopaeans have suggested the thought experiment of determining where exactly the limit of one's mind is. If the mind has no fixed definite limit, and because two things, both without limit are exactly the same, then we could say that the universe and mind are one. Thus, by acquiring knowledge, the individual becomes more like the whole, or holographically comprises a better picture of the whole. Again, this is only an analogy, even though it might have concrete meaning in a higher density.