Round Lot . An order to buy or sell in multiples of 100 shares.
Odd Lot. An order to buy or sell that involves less than 100 shares.
Market Order. An order to buy or sell at the best price currently

 available.
Limit Order. An order to buy or sell when and if a security reaches a

specific price.
Good Til Cancelled (GTC) Order. An order to buy or sell at a specific

price until the investor cancels the order.
Scale Order. An order to buy or sell a security that specifies the total amount to be bought or sold at specified price variations.
Stop Order. An order to buy at a price above or sell at a price below the

current market. Stop buy orders are generally used to limit or protect

unrealized profits on a short sale. Stop sell orders are generally used to

protect unrealized profits or limit loss on a holding. A stop order becomes

a market order when the stock sells at or beyond the specified price and, thus, may not necessarily be executed at that price.

Immediate or Cancel Order (IOC)

A market or limit order that trades immediately and

automatically cancels any unfilled portion. IOC orders are

eligible for auto execution and residual sweeping of the

book in the Hybrid Market.  There are two types of IOC

orders: those that route to ITS away markets and those

that do not.