A stock order is a request placed by an investor to buy or sell stock according to certain specifications.  Most investors use only a few of the many types of orders available.  The three most widely used orders are market orders, limit orders, and stop orders.

Market Order
An order to buy or sell stock immediately at the best available market price.  With this order, the investor would specify the stock and number of shares, but would not specify the time or price.  It will be executed promptly, meaning within the next few minutes.

Limit Order
An order to buy stock at a specified price or lower.  Or an order to sell stock at a specified price or higher.  Here, the investor specifies the price at which to execute the order.  The limit price is never the same as the market's current price.

Buy Limit Order
This type is used to buy stock at a price that is below the current market price.  This type of order is placed when the investor feels that the price will decline within the next few weeks before bouncing back.

Sell Limit Order
This order is used to sell stock at a price that is higher than the current market price.  The skill in this order is determining how far away from the market price to set the order.

Stop Order
This is an order that becomes a market order to buy or to sell when the stock trades at a specified price.  It is used primarily to limit losses on profitable stock positions.  When the stock's market price reaches the order's stop price, a stop order automatically becomes a market order and is then executed at the security's market price at the time.

Sell Stop Order
An order that is used to protect profits on a long stock position, or when the investor owns the stock.  Thus, when the stock is held by the shareholder and the market value rapidly increases, to protect from any losses from an equally rapid decline, a sell stop order will sell at any indication of a drop.

Buy Stop Order
A buy stop order is used to protect profits on a short stock position.  Concerned that a price rise might cause the investor to lose the gain, placing a buy stop order at a certain level above the market price will ensure against this.

American Depositary Receipts (ADRs)
These are negotiable securities representing ownership of the common or preferred stock of a foreign company that are being held in trust.  These are the easiest way for U.S. residents to invest directly in the stock of foreign companies.  It is not common stock, but it is backed by those common shares of foreign company held for this purpose in trust by a bank in the corporations' home country.  One ADR does not always represent one share of the common stock held in trust.

ADRs are divided into two groups: sponsored and unsponsored.
An ADR is sponsored if the foreign company is directly involved in its issuance in the U.S. markets.  It is unsponsored if the foreign company is not directly involved in the issuance.