A stock market is a market for the trading of company stock, and derivatives of same; both of these are securities listed on a stock exchange as well as those only traded privately.
The profit in the stock is decided by the difference between your buying and selling rate. You can call one as short term and long term investor depending on how long one holds the stock. During market crash, people tend to off load their stocks to escape from incurring loss. A day trader is one who buys and sells the stock on the same day without taking delivery