Trading Pair

A trading pair is the two assets a market quotes against each other, written base first and quote second. A price is always expressed as units of the quote asset per one unit of the base, so buying the base necessarily means selling the quote and the other way round. Two things follow that matter in practice. Each pair is its own order book with its own liquidity, which means the same asset can trade in several pairs on one venue at slightly different prices and with materially different execution quality — a thin pair can be expensive to trade even where a deep pair exists for the same asset elsewhere on the same platform. And a pair quoted against a stablecoin is not the same market as one quoted against a national currency, even where the numbers look similar: the settlement asset differs, and so does what you are left holding.