What the term zero-day protection means?

Zero-day protection is the technology present in Symantec security software, that is able to identify and successfully stop malware even before an according virus-signature is designed.

Zero-day protection attempts to identify potentially harmful code by analyzing its behavior, and particularly by checking the amount and destinations of generated network traffic.

Zero-day protection included in Norton products can significantly improve system security, especially during the periods of time when large number of new viruses is released.

You might be also interested in the virus alerting system called Symantec ThreatCon, that provides real-time information about the level of global security risk and the number of newly identified viruses.