.IOPLIST File Extension
What is a IOPLIST file?
Apple .PLIST file used by Mac OS X; uses the ".ioplist" extension instead of the standard ".plist" extension; used for saving and caching information for Mac OS X Kernel extensions (.KEXT) and other system uses.
IOPLIST files are often compressed by Gzip and saved as ".ioplist.gz" files. You can see examples of such files in the /System/Library/Caches/com.apple.kext.caches/Startup/ directory.