I'm guessing they mean React Server Components, but yeah, it annoyed me too that not only do they not define the acronym, but it appears only once on the page -- the title -- so that it's harder to infer it from context.
Great callout, thanks! Edited. I meant the article more as "if you're already curious about the RSC model and have some LISP background" rather than an introduction to what RSC is, but hopefully spelling it out at least helps with that context.