There is only one file type that uses the .KEY-TEF extension:
Keynote iCloud Presentation
Slide show created by Keynote, the presentation software included with Apple's iWork suite; used as the storage format when the user chooses to save the presentation to iCloud; can be opened by both the iOS and Mac OS X versions of Keynote.
The standard extension used when saving a presentation locally is .KEY. Even though iCloud uses a slightly different save format, it doesn't affect the presentation contents when it's reopened.
NOTE: Pages and Numbers use the "-tef" convention as well with the .PAGES-TEF and .NUMBERS-TEF formats in iCloud.
Updated: August 21, 2015