The bid-ask spread tells us the difference behind the highest bid and the lowest ask. Those who wish to buy the stock submit bids which specify the price at which they would like to buy the stock. Those who wish to sell the stock submit asks that specify the price at which they would be prepared to sell the stock. The difference between the highest bid and the lowest ask is called the bid-ask spread. A large bid-ask spread is usually an indication of volatility or an illiquid market. Bid-ask spreads are typically smaller when it comes to very liquid stocks that see a lot of trading volume on a daily basis.