The dictionary is a file that can contain the project elements: description of data files, items, windows, etc. The dictionary is a convenient way to store the created elements so that they can be re-used in new projects.
When reusing a dictionary element, this element can "subscribe" to the modifications. Whenever the object found in the dictionary is modified, this modification can be applied to all the subscriber objects that can "follow" the evolution of the dictionary.
A dictionary can be associated with a user: it is called the user dictionary. In this case, it can be permanently displayed in the "Dictionary" pane. See User dictionary for more details.
A dictionary can also be used to simplify teamwork: a dictionary shared among several developers can contain procedures, preset buttons. These objects are shared and they can be accessed by all the developers.
The management of developer groupware on the dictionary and on its elements is used to restrict the access to the dictionary (or to its objects) for some developers.