The FlashMessenger in Zend Framework has a bit of an odd name as it has nothing to do with Adobe Flash at all. It is a controller action helper defined in the class Zend_Controller_Action_Helper_FlashMessenger, which is used to store and retrive messages that are temporarily stored in the user's session. This is useful if you want to provide form validation and redirection at the same time as you can print out messages after the page has been loaded. If you are familiar with Drupal then this class acts in the same kind of way as the drupal_set_messages() function.
Because FlashMessenger is an action helper it can be initialized in a number of different ways, however, using the _helper property (the helper broker) of the controller is probably the easiest way. The FlashMessenger can be retrived through the helper broker in the following ways: