It is interesting that you ask this question is a proof cryptocurrency is starting to enter the mainstream and people ask questions. At the moment one of the big trends in cryptocurrencies are stablecoins that are pegged to a stable asset like the US dollar or gold as an example.

The steem dollar was supposed to have this purpose in mind and worth always the 1$ US dollar. You need to know that SBD is not pegged to the real asset and make confuse a lot of newcomers on this platform. At the moment SBD is less than the US dollar because of the long crypto bear market and the price of Bitcoin!

You can start your research on the Tether cryptocurrency that was the first stablecoin pegged to the US dollar.

Let me knows if you need more clarification and have an awesome day. :)