What is ICS? Marek Hrycak March 26, 2019 08:39 Updated Follow The "ICS" file contains information related to calendars. Related articles What does the abbreviation URL mean? What is "iCalendar" (iCal)? What does the abbreviation OTA mean? What is iCalendar? How does the synchronization of reservations via iCalendar work? Comments 0 comments Please sign in to leave a comment.