A ringtone is the tune that gets played when somebody calls.
Like most things on your Android device, ringtones can be customized:
- How to set MP3 ringtone in Android (Nexus S)
- Add New Ringtones, Notifications and Alarm tones on Nexus One
- Where is the default ringtone stored?
- How do I set a custom MP3 as a ringtone for other notifications?
- How can I turn songs from Google Play Music into ringtones?
You can even define different ringtones for each contact: