What does the volatile variable mean?

Ensures that reading a variable always retrieves the most recently written value, and writing is immediately visible to all threads. It is used to guarantee visibility of changes between threads, but does not ensure atomicity of complex operations.

Example:

class SomeClass {
    volatile boolean isRunning = true;

    void stopLoop() {
        isRunning = false;
    }

    void runLoop() {
        while (isRunning) {
            // do something
        }
    }
}

Here, volatile guarantees that changes to isRunning in one thread will be visible to another thread checking this condition in a loop.