Synthetic currency pairs (or synthetic cross currency pairs) are artificial currency pairs which are generally not available in the market. For example, right now there are not any “natural” Ethereum (ETH) to Eroscoin (ERO) markets that we can quote to you. So we’ve generated this synthetic pair.
Synthetic cryptoasset trading pairs can be created when one highly traded currency -- usually Bitcoin (BTC) or Ethereum (ETH) -- which trades with the target currencies, is taken as an intermediary currency.
Cryptocurrencies are traded in “base currency” and “quote currency” pairs (see the tooltips for base and quote currencies on this page). But when trading has to take place for a non-traded (non-quoted) pairs or pairs which do not have enough liquidity, an alternate route is taken to construct price quotes for the currency pair. The pair thus created is known as a synthetic pair. A synthetic currency pair is created by trading two separate currency pairs in such a way as to effectively trade a third currency pair. Usually, Bitcoin (BTC), Ethereum, USD, or a stablecoin is taken as intermediary currency to create any desirable synthetic cross currency pair. For example, the Monero (XMR)/0x (ZRX) pair can be traded by creating a synthetic currency pair from two separate currencies. In this scenario, BTC can be taken as an intermediary currency. To trade the Monero (XMR)/0x (ZRX) pair, the trader would simultaneously buy the XMR/ETH (buying ETH and selling XMR and buy the ETH/ZRX (buying ZRX and selling ETH).
Synthetic currency pairs can be used by financial institutions when they wish to trade pairs that do not have sufficient liquidity to execute high volume orders.