What are Ultra High Relief Coins?

By GovMint :

Ultra High Relief (UHR) coins refer to numismatic coins with a special strike that allows all or some of their design details to be raised significantly above the coin's surface, more so than standard or High Relief (HR) coins, creating a more pronounced three-dimensional, sculptural effect. Ultra High Relief coins are struck multiple times using specially crafted dies to achieve their intricate detail and depth. The process of making UHR coins requires advanced technology and precision, making producing them more labor-intensive and expensive than standard and High Relief coins. As a result, their value often reflects more than just their precious metal content alone accounting for their specialized minting process in addition to other numismatic factors.

Sources Used:

 https://louisianastatemuseum.org/museum/new-orleans-jazz-museum-old-us-mint