WaitFor is a procedure that forces the TIdNotify instance to wait until the threaded notification list has a chance to execute the object instance. 

WaitFor examines the notification list in the global variable GNotifyThread. If the current object instance is present in the notification list, the method waits for 10ms (milliseconds) and rechecks for the current object until is has been completed and freed. 

WaitFor is used when the notification thread is executing, and during finalization for the Indy library.

GNotifyThread