Ultra sound money is an Ethereum meme focusing on the likely decrease of the ETH supply.
If capped-supply gold is sound, decreasing-supply ether is ultra sound.
Ultra Sound Money is a project that promotes the concept of Ethereum's decreasing supply through mechanisms like fee burn, which destroys ETH base fees paid for transaction inclusion on Ethereum. The project highlights the potential for ETH to become 'ultra sound' money, surpassing traditional sound money like gold.