Background processing allows for offloading time-consuming or resource-intensive tasks from the main request processing pipeline. In ASP.NET Core Web API, you can implement background processing using a background task library like Hangfire or the built-in BackgroundService class. These libraries provide features to enqueue and execute background tasks, such as sending emails, generating reports, or performing data processing asynchronously. By moving such tasks to the background, your Web API can improve responsiveness and avoid blocking request processing for long-running operations.