Shi-BOOST is, I believe, the correct pronunciation. It’s a simple mixture of 3 parts pastry cream to 1 or 2 parts Italian meringue. The two are gently folded together and the resulting cream is used mainly as a filling for large pastries like Paris-Brest or Gâteau St. Honoré. It’s usually piped, but only through large nozzles since lots of pressure has a way of breaking it.
Chiboust was supposedly invented by a pastry chef of the same name, who supposedly lived in Paris in the mid-1800’s. Supposedly. By no coincidence whatsoever it is he who is credited with inventing Gâteau St. Honoré. Why did he call it that? Because his shop was on Rue St. Honoré. Supposedly. However that’s all I know and I can’t find a thing that’s authoritative on the mysterious M. Chiboust. Anyone who does know something about him, please weigh in.