Trending stocks rarely move in a straight line, but instead in a step-like pattern. For example, a stock might go up for several days, followed by a few steps back during the next few days before heading north again. If several of these zig-zag patterns are strung together, and the chart appears to be moving higher with some degree of predictability, the stock is said to be in an uptrend.
Suppose a trader employs scalping to profit off price movements for a stock ABC trading for $10. The trader will buy and sell a massive tranche of ABC shares, say 50,000, and sell them during opportune price movements of small amounts. For example, they might choose to buy and sell in price increments of $0.05, making small profits that add up at the end of the day because they are making the purchase and sale in bulk.

These developments heralded the appearance of "market makers": the NASDAQ equivalent of a NYSE specialist. A market maker has an inventory of stocks to buy and sell, and simultaneously offers to buy and sell the same stock. Obviously, it will offer to sell stock at a higher price than the price at which it offers to buy. This difference is known as the "spread". The market maker is indifferent as to whether the stock goes up or down, it simply tries to constantly buy for less than it sells. A persistent trend in one direction will result in a loss for the market maker, but the strategy is overall positive (otherwise they would exit the business). Today there are about 500 firms who participate as market makers on ECNs, each generally making a market in four to forty different stocks. Without any legal obligations, market makers were free to offer smaller spreads on electronic communication networks than on the NASDAQ. A small investor might have to pay a $0.25 spread (e.g. he might have to pay $10.50 to buy a share of stock but could only get $10.25 for selling it), while an institution would only pay a $0.05 spread (buying at $10.40 and selling at $10.35).

The information contained in this article is provided for general informational purposes, and should not be construed as investment advice, tax advice, a solicitation or offer, or a recommendation to buy or sell any security. Ally Invest does not provide tax advice and does not represent in any manner that the outcomes described herein will result in any particular tax consequence. Prospective investors should confer with their personal tax advisors regarding the tax consequences based on their particular circumstances.

Risk management - Rather than looking for one big trade, the way a trend trader might, the scalper looks for hundreds of small profits throughout the day. In this process the scalper might also take hundreds of small losses during the same time period. For this reason a scalper must have very strict risk management never allowing a loss to accumulate.
You're probably looking for deals and low prices, but stay away from penny stocks. These stocks are often illiquid, and chances of hitting a jackpot are often bleak. Many stocks trading under $5 a share become de-listed from major stock exchanges and are only tradable over-the-counter (OTC). Unless you see a real opportunity and have done your research, stay clear of these.