What are fire and forget tasks ?

I have read the asynchronous actions and polling in Ansible docs. But I could not understand it.

I understand that poll means the time interval after which the status of the job will be checked.

I think Async means the interval for which to keep the connection open. If yes, What will happen after the connection is closed ? Will the task be completed ?

And I really did not understand the fire and forget tasks.

Can somebody please make it a bit clearer with the help of an easy example ?