Steem dollars – This is the currency of the
Steemit platform and is also known as SMD. This is what people send to one another when they upvote posts on Steemit. The reason it’s called Steem Dollar is because 1 Steem dollar represents any amount of Steem required to reach 1 USD depending on the exchange rate at that time (more or less).
However unlike Steem, you can not use Steem dollars outside of the Steemit platform. You will first have to convert your Steem dollars into Steem and only then you will be able to convert that Steem.
The reason Steem dollars were created is because the founders wanted to peg the value of Steem in some way to the US dollar, so that people will be able to trade inside Steemit but not be afraid of exchange rate fluctuations. This way if you trade, for example, 100 Steem dollars you know you’re giving away 100 USD worth of Steem.