Four times a year, usually in January, April, July, and October, thousands of companies report their financial results en masse. These times of year are called earnings season.
Aluminum maker Alcoa earned the unofficial designation as the company to kick off earnings season. The company's advanced accounting system allows it to close its books very rapidly following the end of the quarter. Alcoa for years was the first stock in the storied Dow Jones industrial average to report its earnings each quarter. Alcoa was kicked out of the Dow by shoe maker Nike in 2013 — but even to this day — many investors see Alcoa's report as the start of earning season.
Not all companies follow a calendar year. For instance, retailers generally bring in a vast majority of their sales each year during December. For that reason, many retailers close their books at the end of January, to give them time to tally up their performance in December and give a full report for the year. When a company ends its year, for accounting purposes in a month other than December, it's called a fiscal year.