This means the package includes a registration generator. WinRAR famously uses a file named rarreg.key for activation. A "keyfilemaker" (or keygen) generates this personalized cryptographic key to unlock the premium version.
The specific string you provided identifies this as a pirated version distributed via BitTorrent trackers. The Keyfilemaker WinRAR.v3.91.x64.Incl.Keyfilemaker-CORE--tracker
hidden inside downloaded torrent packages Share public link This means the package includes a registration generator