“[F]ile slack”, or unallocated space ... occurs after a file is deleted. The area where that file was located, which is formally termed a cluster(s), is partially overwritten by a new file. If the new file is smaller in size than the original file, data from the original file, not taken up by the new file, will remain and can be found by a forensic examiner ... Therefore, file slack will show files, or file fragments, that have been deleted by the user and can no longer be accessed.
R. v. Jacques (2012)
2012 CarswellSask 474 (Sask. Q.B.) at para. 23, 24