Mobile application testing involves testing applications developed for mobile devices to ensure they function properly on those devices. It differs from mobile device testing, which tests the core functionality of the devices themselves, like connectivity and battery life. Popular mobile platforms include Android, iOS, Blackberry and Windows Mobile. Testing covers installation, uninstallation, network connectivity, handling of calls/SMS, screen orientation, low memory/battery conditions, and ensuring applications don't interfere with other device functionality. Automation tools can help with testing on actual devices or emulators.