An active job that is requested to be cancelled may enter a staging state called canceling. To request a job to cancel its execution, the cancel() function should be called:

fun main(args: Array<String>) = runBlocking {
    val job = launch {
        // Do some work here
        delay(5000)
    }

    delay(2000)
    job.cancel()
}

Here, the execution of the job will be cancelled after 2 seconds; cancel() has an optional cause parameter. If an exception is the cause of the cancellation, it's a good practice to send it there; that way, it can be retrieved at a later time:

fun main(args: Array<String>) = runBlocking {
    val job = launch {
        // Do some work here
        delay(5000)
    }

    delay(2000)
    
    // cancel with a cause
    job.cancel(cause = Exception("Timeout!"))
}

There is also a cancelAndJoin() function. As its name suggests, this will not only cancel the execution but also suspend the current coroutine until the cancellation has been completed.