What is the most expensive USDT in the world?

Could you please explain to me, in detail, what exactly is meant by "the most expensive USDT in the world"? I'm somewhat perplexed by this phraseology, as USDT, being a stablecoin pegged to the US dollar, is designed to maintain a relatively fixed value. Does this refer to a particular transaction where USDT was traded at an unusually high price? Or perhaps, is it referring to a situation where the market capitalization of USDT has reached an all-time high? Could you clarify this for me? Thank you in advance for your assistance.