ICS is a file type online commonly used for calendar data. Windows Phone 8 doesn’t have support for ICS built in, but it does allow applications to handle that file for you, and given access to your calendar, can quickly add items to your calendar.
This video uses a nice application from Quincy Mitchell named Add to Calendar.
Maybe someday, the OS will have this baked in, but for now, we’re happy that the extensions can be handled by 3rd party applications.
http://scottcate.looplogic.com/windows-phone-8-downloading-ics-files
