CalDAV account?
Under email add acct in settings, there's a calendar section what is: add CalDAV account?
What is this used for?
iPhone 5s, iOS 7.1
A CalDav account is a calendar only account. Some people will set up accounts like google or a private server that hosts Calendars for them, then use the CalDav set up to link to that calendar. Its the same concept of a CardDav account which is also listed on that same page.