#YYDS
"YYDS" is the Chinese phonetic alphabet abbreviation of the phrase "永遠(yuǎn)滴神" — yǒng yuǎn dī shén — eternal God. Internet users use it to express admiration and affection toward their idols, similar to the English slang "GOAT" (Greatest of All Time).
The phrase was trending on social media during the Tokyo Olympics this summer, when people used it to commend China's athletes for their stunning performances.