A link to another calendar is known as an iCalendar link, or "an iCal." Since the late 1990s, iCal has been an open standard for transferring calendar and scheduling information between people and computers. Almost any calendaring tool you're likely to use supports it. When you share your calendar with others, your calendaring programme will generate an iCal link, even if you never see it. When you share your Outlook calendar, for example, the recipient receives only a button to hit, not a link.