scalp

In the case of market manipulation, scalpers may buy a security, then recommend the security to investors and take a profit on the difference between their price and the sales price once the market demand raises the price.

Scalpers may also act as market makers, making a spread between the bid price and the ask price of a security.  The role of market makers is to provide liquidity in the trading of securities, taking bids and settling on prices.  The profits are realized from the difference between the ask price and the bid price on a security.  The arbitrage gain on these spreads is usually small and short-term.

A day trader is a very active securities trader who holds securities for a very short time (generally one day or less). If a day trader wants to scalp, he or she would buy and sell shares when there are small changes in the stock price. For example, if the price of Company XYZ rises from $41.50 to $41.55, the difference is only a nickel. To most investors, that's not a compelling change, but scalpers capitalize on this by buying 100,000 shares at $41.50 and selling at $41.55 for a profit of $5,000. If this price change takes place in the course of just one trading day, which is entirely possible, the trader can make $5,000 in a day. Often, the price changes are even smaller than $0.05 a share for scalpers to profit.