"/etc/shadow-" What is the purpose of this file?

What is the purpose for the file /etc/shadow-
or for the files
/etc/passwd-
/etc/gshadow-
/etc/group-

These files are nearly identical to their
cognates in content and file attributes.
Is there a simple explanation for maintaining
these files along with the standard file:

/etc/shadow, /etc/passwd, /etc/gshadow, /etc/group ?

Is the a common convention for other Unix-like systems?

My reason for asking is that this is a minor inconvenience
when hiding this /etc/shadow- file and what programs may
be using this file.

Jerry M.
a RedHat user