Normally, when the maximum number of applications (applied + confirmed) has been reached, the application form will close.
If you enable waiting list, instead of closing the registration form, people can register for the waiting list. They then get the status “reserve”.
However, even when the waiting list is not enabled, if several people attempt to register at the same time, and the maximum number of applications is reached, some of the registrations will be put on the waiting list. This will be shown in the confirmation page and email.