Rebated Rim
A case design whose rim is smaller in diameter than the case body, found in families such as the .284 Winchester and the WSM cartridges.
A rebated rim is one where the rim and extractor groove are cut to a smaller diameter than the body of the case ahead of them. This lets a designer build a fatter, higher-capacity body while keeping the case head rim at a standard bolt-face size, so existing bolts and magazines can be adapted to a larger cartridge. The .284 Winchester pioneered the idea, and the short magnum families later used it to fit big powder columns into compact actions.
Like a rimless case, a rebated-rim cartridge usually headspaces on its shoulder rather than the rim. The tradeoff is that the smaller rim gives the extractor less purchase, so feeding and extraction reliability depend more heavily on a well-fitted bolt face and a properly tuned action.