In my experience Outlook is one of the most underutilized of the essential MS Office programs. Tasks usually make their way to the learning curve after email, contacts and calendar. A task is an item that you create in Outlook to track until its completion. It can also be described as an electronic to-do-list.
Unlike a calendar item, tasks remain visible until completion or deletion. They are always on your to-do-list which is visible while in email (enable it on the View tab), calendar (weekly or monthly view), or tasks.