Earlier quoted context omitted.
But they are not backed by real USD, and Tether themselves have admitted as much: their FAQ now states simply that it's backed up by "Tether's reserves", which apparently consist of other cryptocurrencies.
Please link your sources, their reserves as I understand may in some part consist of unspecified collateral, even if they are crypto which I seriously doubt due to its volatility the fact remains that Tether is trusted enough to be supported by the majority of major exchanges. The imminent demise of tether has been predicted for many years now. You can short tether at Kraken or choose to use one of the many other USD…
https://cointelegraph.com/news/changes-to-tethers-terms-of-r...
https://bitcoinmagazine.com/articles/holders-are-not-at-risk...
Note that all of this is over a year before the Tether printer kicked into overdrive around April this year and started inflating from $4B to the current $18B+.