Deep freeze is a program which creates a hidden partition identical to the one you want to 'freeze'. This way the information that is on one 'frozen' partition, if modified or deleted or moved, it will be restored as it was when you frozen it. All the information that you put on that disk will be deleted.
So this software is being used in schools where kids often delete some system files or some files from the Borland C 3.0 compiler so it won't work any more, or install games or other software. Deep freeze will restore the deleted files and uninstall the games and so on, with just a restart.