There is only one file type that uses the .TAR.Z extension:
Zipped Tarball File
A TAR.Z file is a Unix TAR archive compressed with a standard Unix compression algorithm to save disk space. It contains one or more compressed files. The file is commonly used on Unix operating systems to archive groups of files.
Tar zipped files more commonly use the .TAZ and .TZ file extensions.
Updated: April 12, 2016