In Java, a daemon thread is a type of thread that runs in the background and provides a supporting role to other threads in the application. A daemon thread is automatically terminated when all non-daemon threads have completed.

Daemon threads are typically used for tasks that do not require a long running or continuous process. For example, a daemon thread could be used to monitor some event and perform a specific action when the event occurs. Since a daemon thread does not prevent the JVM from exiting when all non-daemon threads have finished, it can be useful in cases where you do not want the application to continue running once the main thread has completed.

In Java, you can set a thread as a daemon thread by calling the setDaemon(true) method on the thread object before starting the thread. Here's an example:

Thread myThread = new Thread(() -> {
    // Thread logic goes here
});

myThread.setDaemon(true);
myThread.start();

Once the thread is set as a daemon thread, it will run in the background until the application is terminated or until all non-daemon threads have completed. It's important to note that a daemon thread should not perform tasks that are critical to the application's functionality, as the thread may be terminated abruptly if all non-daemon threads complete before the task is finished.