Artaud's body without organs
The body without organs and the organs–partial objects are opposed conjointly to the organism. The body without organs is in fact produced as a whole, but a whole alongside the parts—a whole that does not unify or totalize them, but that is added to them like a new, really distinct part.
...
The organs–partial objects and the body without organs are at bottom one and the same thing, one and the same multiplicity that must be conceived as such by schizoanalysis.
(Gilles Deleuze & Félix Guattari, Anti-Oedipus p.326)
"The whole is another part among its parts" is something I've been saying for years. They go into more detail about how to conceptualize this metaphysically in A Thousand Plateaus, but this is pretty straightforward. What the body without organs is opposed to is not organs in the sense of partial objects (Melanie Klein's "part-objects"), it's opposed to organs as components of the organism as a totalizing entity.
Deleuze and Guattari borrow the term "body without organs" from the radio play To Have Done With the Judgement of God, by Antonin Artaud. The play was recorded while he was alive, only a few months before his death, but pulled from broadcast and not actually aired until years later. It ends with:
Man is sick because he is badly constructed.
We must make up our minds to strip him bare in order to scrape off that animalcule that itches him mortally,god,
and with god
his organs.For you can tie me up if you wish,
but there is nothing more useless than an organ.When you will have made him a body without organs,
then you will have delivered him from all his automatic reactions and restored him to his true freedom.They you will teach him again to dance wrong side out
as in the frenzy of dance halls
and this wrong side out will be his real place.
When Artaud said there is nothing so useless as an organ, D&G take him as having meant that the body without organs is not composed of organs as parts the way the body as organism is; instead it's just as partial as the organs, and despite fitting over them, it effectively has no use for them as parts. From the vantage point of the body without organs, there is no hierarchical relationship between the body and "its" organs. There is no organ-ization of the body, no dominion of the body over the organs. This could be related to catatonia, which Artaud likely experienced, but the metaphysical and the psychological are closely linked for D&G.
Manuel DeLanda describes Deleuze's metaphysics as a "flat" ontology, meaning that it rejects the hierarchies of being found in platonic philosophy, which still infect western culture so deeply as to be intuitive common sense for most people. For D&G, the body is never on a level above its organs, the organs aren't above their cells etc. And neither is the mind or soul above (or even distinct from) the body. Experience is not a higher order of being when compared with matter, and all matter experiences to some extent (though not exactly in the sense of pansychism).
(Alfred North Whitehead has some similar ideas, but it's been too long since I read his book and I can't remember exactly how the concepts worked lol)
Similar to how Buddhism says one needs to let go of the idea of substance or experience as something that is "mine," D&G seem to call for realizing that there is no transcendent belongingness of anything to anything else. All belongingness exists only at the level of representation. And it's also at the level of representation that power operates, that one is given a model of what to do and what to be, and judged according to deviation from that model. "Automatic reactions" are actually taught, programmed into the body, and they stand in the way of realizing that the body is not the body, it is the entire world.