Files with the BZ extension are archives compressed most often with the unix bzip utility. BZ files are created based on the Burrows-Wheeler and Run-Length (RLE) algorithms. The latter method is a fairly simple, lossless compression method that uses a repeat count of the same file contents.

BZ is a format that is used on Unix and Linux (various distributions). Files of this type are created from TAR archives. There is one archived file (usually a TAR) in a BZ file.