Limit order

From Financial Literacy Wiki

Limit order is an order to buy a security (eg. stocks, bonds) at not more, or sell at not less, than a specific price. This gives the trader control over the price at which the trade is executed; however, the order may never be executed (or filled) depending on the security trading movement.

A buy limit order can only be executed at the limit price or lower. For example, if an investor wants to buy a stock, but doesn't want to pay more than $20 for it, the investor can place a limit order to buy the stock at $20 "or better". By entering a limit order rather than a market order, the investor will not buy the stock at a higher price, but, may get fewer shares than he wants or not get the stock at all. A sell limit order is analogous; it can only be executed at the limit price or higher.

Both buy and sell orders can be additionally constrained so do check with your trading securities companies.