Earnings season is the six to eight week period each quarter where the majority of U.S. companies report quarterly or annual earnings.
Just as there is a holiday season running from (roughly) the end of October through the first of January, there is earnings season for those who follow the antics of Wall Street. However, while the holiday season happens only once a year, earnings season happens four times. Luckily, nobody (except maybe analysts) expect presents.
There are roughly 5,000 companies publicly traded in the U.S. On the S&P 500 itself, there are, of course, 500. On the Nasdaq there are about 3,000. Not all of these, of course, are followed by analysts, but many of them are.
With many, even most, following a calendar year as their fiscal year, that means that they mostly report quarterly earnings in May for the March quarter, August for the June quarter, November for the September quarter, and February for the December quarter.
With that many companies reporting in such a short time span, things get pretty hectic. Analysts and financial reporters both look forward to and dread earnings season. They have to listen to conference calls, update their valuation models, and issue new and improved upgrades and downgrades. Reporting services (such as The Motley Fool) are reporting and analyzing the reports.
In short, we live for this stuff!
Although earnings season fills the media with the lastest information from companies, the period immediately before reporting is a quiet period when companies are not allowed to say anything about earnings (while they close their books and collect the numbers to be reported). This period of little news lends itself to more speculation and rumors reported as news. In German this season is often called sauergurkenziet (sour pickle time), usually translated at "silly season."