A calendar is an instance of the Data-Admin-Calendar class, which records the work schedule of an organization or group of people, including holidays and shift start and stop times.
Calendar data instances can be referenced in organization, workbasket, and Operator ID data instances, and in service-level agreements. In the context of a calendar, due dates and similar calculations can be based on business days rather than calendar days.
Two standard flow actions SendMeetingRequest and GetAppointmentListallow direct interconnection with the appointment calendar in Microsoft Outlook.
See PDN article Integrating with Outlook calendars.