Microsoft Outlook supports three forms of scheduled activities on your calendar: appointments, events and meetings. Networked Outlook installations enable others to schedule these activities for and with you.
An appointment is a scheduled block of time that only involves you. The hours are blocked out on your schedule, but it does not include other attendees or resources. Your calendar will show the appointment framed between the start and end times.
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Once an appointment goes over 24 hours in length, it becomes an event. The event entry does not block out the hours on your calendar and your time continues to show as free. The calendar marks the event by placing a banner at the top of the date on which it occurs.
A meeting is an activity that involves you and others during the same blocked time period. Outlook allows you to set meetings that affect the calendars of other people. A meeting may also schedule resources, such as meeting rooms.