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
While the specific contents of a file named "RP14" depend on its source, these terms frequently appear in the following contexts: Collections or "Redux Packs" (RP) for The Sims