When you are about to place an order to sell a stock you have the option to sell when the stock price increases. You will then be asked to set a specific stock price. This means your order will only be executed when the price of the stock you are about to sell is at or above the amount you specified.
This type of order is called a Limit Order. Limit Orders are only good for the day; this means that if that stock does not cross the price you set by the close of the stock market that day, the order will be canceled.