What is bid-ask spread?

 The bid-ask spread is the difference between the lowest ask and the highest bid. As you'd imagine, a low bid-ask spread is desirable for liquid markets. It means that the market has good liquidity since inconsistencies in price are continually brought back to balance by traders. In contrast, a large bid-ask spread usually means that a market is illiquid, and there is a large difference between where buyers want to buy and where sellers want to sell.