Notification sound / Default notification
This option allows you to set the default sound to be played when you receive a text message or other notification for which you have enabled sounds, such as an incoming email. Note that this notification sound may be overridden elsewhere. For example, it is possible to set a notification sound within the Text messages app, or the Email app, or other apps that can receive notifications.
Tones are chosen in the same manner as in the Ringtone option above.