A Notification is a message that pops up on the Time Tracker User's phone to alert him/her about specific items of interest. For example, you can configure the Time Tracker to send a Notification to the User whenever a new Project or Job is assigned to him/her. These notifications appear on the user's phone, even when the screen may be closed or when the user is not within the Time Tracker app. All Notifications also appear within the Messages screen inside the Time Tracker.
You can configure when Notifications are sent to the User. You can also configure what fields / information are sent to the User. These items are configured within Salesforce by an Administrator.