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 is likely an obfuscated or encoded title of a film or television show. "D0sS0n" often replaces letters with numbers (Leet Speak), suggesting the word "Dos Son" or "Dissonance." "Mlt1tud" likely translates to "Multitud" (Spanish for "Multitude"). D0sS0nMlt1tud.m720p.yamil.part3.rar
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 This is the handle of the original uploader