What does concurrent rendering mean in React?

Direct answer

Concurrent rendering means React can prioritize, pause, resume, restart, or abandon render work before committing it, allowing urgent interactions to stay responsive while lower-priority UI is prepared.

The important property is that rendering can be interruptible. React may begin calculating a new tree, pause that work when something more urgent arrives, and continue or restart later.

Render phase: React calculates what the UI should look like and may interrupt this work.
Commit phase: React applies the finished result to the host environment; it does not commit a half-finished tree.
User experience: urgent input can remain responsive while expensive non-urgent UI is prepared in the background.