Jacob Franks, via email
This file appears when you perform an Archive And Install installation of Mac OS. The installer places a variety of system files – such as preference files, fonts and plug-ins – in this folder. You can’t boot your Mac from here – it’s there simply for the storage of old system files.
If your Mac performs oddly after installing a new operating system you can rummage around in this folder and retrieve the goodies you’ve lost. If you’ve run your Mac for a month or more and everything is tickety-boo, it’s safe to delete the folder.