With stocks, a request from a customer to buy or sell a stock, that, if not cancelled or executed the day it is placed, expires automatically. For example, with a day order to buy a stock at $50 or better, and the stock never rises above $50, the order is not filled and expires as worthless. See also good-till-cancelled order.
A trader who makes many trades through a trading day, buying and selling positions in order to profit from short-term changes in prices. Duration of trades is a few minutes to a few hours, and rarely held overnight. Day trading is considered high risk because there is no guarantee that price will move in the short term desired direction, and transaction costs mount up with this more frequent trading style.
An individual who acts as a principal or counterpart to a transaction. Principals take one side of a position, hoping to earn a spread (profit) by closing out the position in a subsequent trade with another party. In contrast, a broker is an individual or firm that acts as an intermediary, putting together buyers and sellers for a fee or commission.