A possible backup file was found on your webserver. These files are usually created by developers to backup their work.
Backup files can contain script sources, configuration files or other sensitive information that may help an malicious user to prepare more advanced attacks.
Remove the file(s) if they are not required on your website. As an additional step, it is recommended to implement a security policy within your organization to disallow creation of backup files in directories accessible from the web.
Testing for Old, Backup and Unreferenced Files (OWASP-CM-006)
Security Tips for Server Configuration
Protecting Confidential Documents at Your Site