A cluster that is not currently occupied by any data. This space may contain residual data from the file that previously occupied this space. The space may also contain signatures of a volume being deleted, damaged or re-formatted.
Active@ Partition Recovery supports detection of signatures for NTFS, exFAT, FAT, Linux Ext2fs/Ext3fs/Ext4fs, Apple HFS+ and Unix UFS volumes.
See also: cluster