This is usually a shorthand code or abbreviation for the title of the content.
Because this is only "Part 1," you won't be able to open or play it on its own. You will need to download all the subsequent parts (Part 2, Part 3, etc.) into the same folder. Once you have the complete set, you can use a program like WinRAR or 7-Zip to extract the actual video file. t0a2022 MULTi.1080p.R-MG.part1.rar
This indicates the file contains multiple audio tracks (often several different languages). This is usually a shorthand code or abbreviation