[nojvek]

Isomorphic - runs the same on both web browser and server nodejs.

Virtual dom - not the real dom tree but a representation of the dom using nested objects. You can diff two versions of trees (current and updated) and apply the changes to the real browser dom. This makes building pretty UIs super easy since a view is essentially a function of state. Diffing the virtual dom and patching the real dom is much faster than iterating over the the real dom for every update.

On the server side, you use the virtual dom to render to html string.

So true isomorphism is basically when the same code is used in both browser and server. Server renders the initial page load to html string, once loaded by the browser the browser again uses the same view code to make further UI changes without causing a page reload (single page app). Good for search engines and crawlers, good for blazing fast performance and instaneous interactivity.