$ATEHUN is short for $ATEHUN'dred. It's derived from the first organic meme around Hyperliquid: $800/pt. $800/pt was based on Adair's long tweet thread that gave the bull case for Hyperliquid before they had a token and they just had a points program to award users
Essentially, he argued it was likely the best opportunity in crypto and is destined to be a top 10 coin which would make each point worth $800 in the next 12-18 months. $ATEHUN represents this undying delusional bullishness on Hyperliquid as the future of finance.