How do you spell relief? If it's for the ArtCAM software, it's RLF. This is the format of relief models in ArtCAM (an Autodesk program discontinued as of 2018), and is one of the formats used for models to be 3D printed.
It would be nice to find some to link to. A search under such queries as "ArtCAM RLF file free download" gets pages and pages of results, but they all seem to have their downloads behind a registration wall, or are bait-and-switch links leading to a site with paid downloads, or are some kind of sketchy thing that seems certain to be an outright scam or malware, and an abundance of caution keeps the researcher from going far enough into them to verify this for certain. Clearly this file type is popular enough to draw out those who want to exploit people looking for them. If anyone can find downloads with no strings attached or hoops to jump through, or provide a few on their own site to link to, that would be appreciated.
(Somebody did upload one to a forum thread here; whether this is at all a "typical" RLF file is unknown.)