Company earnings reports
It's like a bonus your boss hinted at in advance: everyone roughly knows the amount. The only surprise is whatever doesn't match the expectations.
In a report, people look at three things: how much the company sold, how much it earned, and what it promises for the coming months. The last one is often the most important: the market buys the future, not the past.
How often do large American companies report?
Why is it dangerous to hold a stock trade through a report?