Tether (USDT) is a type of cryptocurrency known as a stablecoin. It is designed to maintain a stable value by pegging its price to a specific fiat currency, typically the US dollar. Each tether token is meant to represent one unit of the currency it is pegged to.

The purpose of tether is to provide users with a digital asset that retains the stability of traditional fiat currencies, while still being able to take advantage of the benefits of blockchain technology. It allows users to easily transfer and store value digitally, without the volatility often associated with other cryptocurrencies.

Tether is commonly used in the cryptocurrency market as a way to quickly move funds between different exchanges or wallets, as its value remains relatively constant compared to other cryptocurrencies. It is also used as a trading pair on many cryptocurrency exchanges, allowing users to trade other cryptocurrencies against tether.

It's important to note that while tether aims to maintain a 1:1 ratio with the fiat currency it is pegged to, there have been some controversies and concerns regarding its transparency and the actual reserves backing the tokens.