There are two additional calendar types beyond primary calendars for individual users and generic accounts. Please see the table below for benefits and limitations for each type..
User Created Calendar
A User Created Calendar is associated with a primary user calendar, but it has separate permissions. They can be used to track schedules, projects, etc.
Resource Calendar
A Resource Calendar represents a physical resource, like a conference room or piece of equipment. They are available on the "Rooms" tab of a Google Calendar event.