If checked the option "Always create backup copy" under Settings -> Save within Microsoft Word 2016 on macOS, when editing a docx file, a folder named as same as docx file name(without ext) will be created and placed a docx backup file named "Backup of DOCX_ORIGINAL_FILENAME.docx".

Continuation of https://github.com/github/gitignore/pull/594/ and details from http://support.microsoft.com/kb/211632