Occurrences or system notifications provides a way to communicates with you, yours customers/members and/or an existing platform. Most plugins support notifications through specific event names which are triggered based on some action being performed.
    
You can setup email notifications for you and your customers or an API callbacks to interface and communicate with an existing platform and/or website. The list of system notifications is continuously being expanded.  Lets take a look at the existing occurrences, when they are trigger and examples of what can be achieved.
    
Note: Some plugins may not support occurrences for your administrative portal.