There are two well-known types of data recovery - unformat and undelete.
The term "undelete" almost always describes a recovery of one file, or a couple of files from an otherwise properly functioning filesystem.
"Unformat" typically describes a recovery of multiple files off the massively damaged volume when none of the data is accessible any longer.
The "undelete" process utilizes the fact that the volume is mostly in good condition, all but one sought-for file.
Unlike the above, during the "unformat", the data recovery software must be able to handle some massive inconsistencies in the partition, since even the quick format would overwrite parts of the filesystem.
It is in most cases useless to use some file data recovery software on files recovered by unformat. The "undelete" is usually very quick and in most cases provides more usable recovered files.
