Is USDT tether the same as USD?

Could you clarify for me if USDT tether and USD are interchangeable terms? I've been hearing a lot about digital currencies recently, and I'm trying to wrap my head around the nuances. As I understand, USD represents the official currency of the United States, a globally recognized and widely used fiat currency. On the other hand, USDT tether seems to be a digital representation or token pegged to the value of the US dollar. However, I'm not entirely sure if they serve the same functions or if they can be used interchangeably in transactions. Is USDT tether simply a digital version of USD, or does it have its own unique properties and uses within the cryptocurrency and finance landscape? Could you please elaborate on the differences between the two, if any, and how they might be applied differently in practice? Thank you for your assistance in clearing up this confusion for me.