What is the difference between async mode and concurrent mode?

Both refers the same thing. Previously concurrent Mode being referred to as "Async Mode" by React team. The name has been changed to highlight React’s ability to perform work on different priority levels. So it avoids the confusion from other approaches to Async Rendering.

Practical Code Example

// Async Mode vs Concurrent Mode:
// React 18 Concurrent Rendering allows React to interrupt a long render to process urgent user input (typing).