lost cluster

Also called a lost allocation unit, or a lost file fragment. A data fragment that does not belong to any file, according to the system's file management system, and, therefore, is not associated with a file name in the file allocation table. Lost clusters can result from files not being closed properly, from shutting down a computer without first closing an application or from ejecting a storage medium, such as a floppy disk, from the disk drive while the drive is reading or writing.