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