The bid and the ask price in the stock market are the maximum price someone wants to pay for a certain share and the minimum price someone is willing to sell a share for, respectively. Bid and ask prices are determined by supply and demand which are tracked by stock exchanges during opening hours. Where there is a high demand for shares of a fund, or specific stocks, there will be more buyers than sellers. As a result, this may push the price of shares up. Conversely, if more investors are selling their shares than there are buyers, then the price will likely fall.