FWIW those of us in the JavaScript community who don't care to create buzzwords for everything call it JavaScript. No Isomorphic, no Universal. There's nothing different. It's just JavaScript.
On the client you wouldn't use `fs` module, but on the server you wouldn't use jQuery unless you were manipulating the dom through scraping with Cheerios.
It's still JavaScript, but how you design/write it is fundamentally different when you're writing for both the client and server.