TL;DR Earnings season is the few weeks each quarter when most public companies report results. Reports land outside market hours, expectations are pre-loaded, and stocks gap up or down overnight in response.
The plain-English version
Public companies must report their finances every quarter, and their fiscal calendars cluster — so about 2–6 weeks after each quarter ends (mid-January, mid-April, mid-July, mid-October), reports pour out daily. Big banks traditionally kick things off; mega-cap tech mid-season is the main event.
Each report is a bundle: revenue, EPS, margins, and — often the real market-mover — guidance, management's forecast for what's next. A quarter is history; guidance is the future, and markets price the future.
Why stocks jump or crater overnight
Companies report before the open or after the close, never mid-session. Reaction happens in after-hours and pre-market trading, so regular-hours holders wake up to a done deal: +9% or −13%, no ordinary exit in between. Earnings are scheduled volatility — dates are public months ahead, which is why options get expensive into them (see: IV crush) and why "holding through earnings" is a deliberate risk decision, not a detail.
How to actually read a report (fast)
The market's checklist, roughly in order: revenue vs consensus, EPS vs consensus, guidance raised or cut, margins, and one or two company-specific metrics (subscribers, deliveries, cloud growth — every company has its "one number"). The earnings call afterward — executives grilled by analysts — routinely moves the stock a second time.
The common mistake
Believing good results guarantee a green day. Stocks move on results relative to expectations that were already priced in — great numbers that were anticipated can sell off ("sell the news"), and a decent report from a hated stock can rip. Every season, someone learns this with real money. Cheaper to learn it here.
Educational only — not investment advice. Earnings season rewards preparation and punishes vibes, quarterly.