$JE Read that explaination: Definition of 'Depth' The ability of a security to absorb buy and sell orders without the stock price dramatically moving in either direction. Depth is closely related to the liquidity of the market. A deep market can be expected to absorb larger buy and sell orders before an order moves the prices. Generally, deep markets will have smaller bid-ask spreads because of the increased competition among market makers for order flow. Also referred to as "market depth."