Read interesting day trading articles and other investing-related writings written by professionals. Bid: This is the price a buyer is willing to pay for your security. Ask: This is the price for which a seller is willing to pay his security. Open: Price of a stock when the market opens for trading. Close: Last price of a stock in the trading day. Short Selling: A short sale is a sale of a stock you do not own. Investors who sell short believe the price of the stock will fall. If the price drops, you can buy the stock at the lower price and make a profit. If the price of the stock rises and you buy it back later at the higher price, you will incur a loss. Click here for some more information about it.