A busy loop in Node.js occurs when a long-running or infinite loop keeps the event loop busy, preventing it from handling other tasks like I/O operations. This can make your application appear frozen or unresponsive, especially when there are no `await` or `setTimeout` statements to yield control back to the event loop. To fix this, you need to refactor any blocking synchronous code into smaller, non-blocking chunks. For example, if you’re iterating over a large array or performing a computationally expensive task, you can break it into smaller pieces and use `setImmediate()` or `process.nextTick()` to allow the event loop to process other tasks in between iterations. Alternatively, offloading heavy computations to worker threads can help free up the event loop. Profiling tools like `0x` or `clinic` can help identify sections of the code where the event loop is getting blocked. Understanding and avoiding busy loops ensures your application remains responsive even under heavy load.