During the trading day, a price chart looks continuous, as if a stock only moves while the market is open. In reality, news keeps arriving after the closing bell and over the weekend — earnings, economic data, company announcements — and prices keep reacting to it. By the time the next regular session opens, a stock can be trading at a noticeably different price from where it closed.
What an opening gap is
When the regular session opens above or below the previous day's close, that jump is called a gap — a gap up if it opens higher, a gap down if it opens lower. Some trading does happen in between, in the pre-market and after-hours sessions, but it is much lighter than the regular day, so the gap mostly reflects opinion shifting while the main market was closed.
Extended hours are thinner
Many venues let people trade before and after the regular session, but far fewer trades happen in those intervals. With less trading going on, prices can move more sharply on smaller amounts of activity, so an extended-hours price can be less representative than one from the regular session.
How this shows up on Investment Bets
A bet that reaches its target date closes automatically at that day's regular-session closing price. If the stock gapped at the open that morning, the whole day's trading — including the close — starts from that new level, not from where it closed the day before. The app can look quiet while markets are shut, but the overnight and weekend risk to your open positions is still there.