“AES” meaning “actually existing socialism.” The debate over this word goes all the way back to Engels at least.

Someone else may help me find a link, because I remember reading a different article about this specifically, but these three definitely touch on it:

https://redsails.org/tankies/

https://redsails.org/brainwashing/

https://redsails.org/losurdo-on-totalitarianism/ (this one is about “totalitarianism” and the “horseshoe” theory I referenced above)