Is an investor who buys and sells securities / instruments and holds these for short periods of time. Traders often make very many and frequent trades so that they can profit from quantity.
There are different types of traders, and they are often classified according to how short periods of time they hold the shares. The most common are:
Day-trader - as the name implies, they do not hold the securities / instruments longer than one day
Swing trader - is happy to hold the securities / instruments for a few more days, to weeks at a time.