.BZ File

The bz file extension is sometimes used for BZIP compressed file archives. 

Occasionally used for archiving data on Unix systems and for exchanging files on the internet. Binary format. Compresses data using a combination of the Burrows-Wheeler transform and Huffman entropy coding. Stores a single file. Typically used in combination with TAR. Developed and maintained by Julian Seward.

MIME types:
application/x-bzip

Files with bz file extension can be sometimes found as renamed BZIP archives on Unix systems. Same format, just different extension.

How to open:

Use any file archiver with BZIP support.

How to convert:

Probably can be converted to other formats.