Collections or "Redux Packs" (RP) for The Sims 4 often use similar naming conventions for custom content or mod updates.
The file is the third part of a split RAR archive, typically used to distribute large datasets, software, or media collections that have been divided into smaller pieces for easier uploading and downloading. RP14.part3.rar
To access the contents of this file, you generally need to have of the archive (e.g., part1, part2, and part3) in the same folder. You then open the first part with a file extractor such as WinRAR , 7-Zip , or The Unarchiver , which will automatically combine them into the original full file. Contextual Uses of "RP14" and "RAR" Collections or "Redux Packs" (RP) for The Sims