This specifies that the file is the third part of a larger split archive. You will need all parts (e.g., part1, part2, part3) in the same folder to successfully extract the video using a tool like WinRAR or 7-Zip. What You Should Know Before Extracting
You cannot open or play Part 3 on its own. If you are missing Part 1 or Part 2, the extraction process will fail. D0sS0nMlt1tud.m720p.yamil.part3.rar
This is the handle of the original uploader or encoder, a common practice in the "warez" and release community to identify the source of the rip. This specifies that the file is the third