Shared calendars are displayed side by side with your own calendar (which is called "Calendar").
When you opened the shared calendar, Outlook would display it side by side with your own. If you were sharing calendars with a group of people, your screen could get crowded. To hide a calendar, you would clear the check box for that calendar under Other Calendars. The name would remain in the list, so you could always view as many calendars—or as few—as you wished.
For your convenience, Outlook displays each calendar with its own background color, both in the list of sharers and when you view the calendar. If you like, you can reorder the calendars in the list by dragging them.