: The "B" is simply the name of the original archive. The ".7z" indicates the compression format, and ".005" indicates its position in the split sequence.
: This specific file ( .005 ) is not a complete archive on its own. You cannot open it unless you have all the other parts (at least parts .001 through .004 , and any subsequent parts) in the same folder. B.7z.005
The file is the fifth part of a multi-volume compressed archive created using the 7-Zip software. : The "B" is simply the name of the original archive