What are iPhone badges?
The iPhone uses badges to indicate that a new message, email, push notification, or voicemail is waiting. Each app with new unread information has a white number with a red background in the upper right hand corner of the app icon. This is a badge.
When missed calls are viewed, voice mails are listened to, and SMS messages are read, the badges will count down accordingly or disappear when all pending information has been seen.
Push notification badges can be turned off or on for each individual app supporting push notifications. Some other apps such as RSS readers will show a badge indicating how many unread stories are listed in all news sources as of the last update.