What Does Brilliant Uncirculated (BU) Mean in Coins?

By GovMint :

In the world of coins, "Brilliant Uncirculated" (BU) signifies a coin that has never been circulated and retains its original mint luster and detail. These coins exhibit a brilliant sheen and sharp details. In the realm of numismatics, the term "Brilliant Uncirculated" (BU) extends beyond the physical condition of a coin to encompass its overall presentation and appeal. A Brilliant Uncirculated (BU) coin not only retains its original mint state but also exudes a captivating radiance that sets it apart from circulated coins.

Sources Used:

 https://www.usmint.gov/coins/coin-medal-programs/ultra-high-relief-double-eagle