Pre-market and after-hours
Pre-market and after-hours are the trading windows before and after the regular session. They exist because much of the news that moves a company, starting with its results, is published outside regular hours. They carry far less volume than the session, so spreads widen and a spectacular move can rest on very few trades. An 8% jump after hours is not a reliable guide to where the stock will open the next day.
See also
See it on real data
Celsmar computes this from the accounts companies file with their regulator, and shows which line every figure comes from. Free to start, no card.
Definition for informational purposes. It is not financial advice nor a recommendation to buy or sell.