Here you can see a list of all priorities that can be selected in the Priority property of tasks and information about them. Priorities are assigned to tasks to indicate how urgent they are.
You can manage the priorities in the list using the appropriate icon on the left side: Edit () or Delete (). The Move up () and Move down () buttons can be used to change the order in which the priorities are available.
New priorities can be created by using the New task priority link.
More resources can be found in Developer's Guide -> Modules -> Project management -> Overview.