Tether is a cryptocurrency which is backed by an equivalent amount of US Dollars. That allows traders to quickly move an equal amount of fiat (USD) between different exchanges. Bank wires may take up to 5 business days to be received and added to your trading balance. Tether, on the contrary, allows you to move funds in a couple of minutes. That makes trading a way smoother and faster allowing to adjust your trading strategy to a constantly changing conditions.
Tether issues tokens based on both Ethereum and Bitcoin blockchains. On DSX you can easily exchange two version from one to another. More details in that article.