A resource calendar is the calendar of a mailbox for which the parameter "
AutomateProcessing" has been set to "
AutoAccept". Because user mailboxes use a fixed value of "
AutoUpdate" for this parameter, user mailbox calendars can never be resource calendars.
What makes a resource calendar different is the ability to set specific parameters on the containing mailbox that governs the handling of meeting items. By default, for example, a resource calendar will replace the subject of a meeting with the organizer's name and delete attachments and notes of the item stored in its calendar.
A description of these and other options can be found in the Parameters section of the TechNet Set-CalendarProcessing article