Every business has its own special language, and day trading is no different. Here are a few terms you may come across:

• Fibonacci series: The Fibonacci series is a list of numbers, each of which is the sum of the two numbers before it. It stretches into infinity but starts like this: 0, 1, 1, 2, 3, 5, 8, 13. Proportions based on the Fibonacci series show up throughout nature, and many believe that they indicate profitable trading opportunities.

• Kelly criterion: Want to trade with a guarantee of success? It's mathematically possible using the Kelly criterion. In its simplest version, the percentage of your account that you trade is equal to the probability of the trade going up minus the probability of it going down. If your testing shows you that a strategy works 60 percent of the time and fails 40 percent of the time, then each time you trade with it, you would trade 20 percent of your funds: 0.60 – 0.40.

• Pattern day trader: Regulations define this as someone with at least \$25,000 on account, who executes four or more day trades within five business days, with those trades representing more than six percent of the customer's total trades. This is important for how the brokerage firm handles margin activity.

• Wash-sale rule: The wash-sale rule is a tax trap that catches many day traders. It says that if you sell a security at a loss, you can't deduct the loss if you buy the same security 30 days before or after the sale. Day traders might buy and sell the same security several times in one day. There are ways around the wash-sale rule, but they require some planning and careful recordkeeping.