Pre-trading and post-trading refer to the transactions during the abnormal opening period. The transactions before the opening are called pre-trading and the transactions after the closing are called post-trading. In the United States, the new york Stock Exchange and Nasdaq have special trading hours before and after the opening.
Generally speaking, the trading volume of US stocks before and after the market is not very high, the liquidity is not strong, and the bid-ask spread is relatively high. After-hours trading is equivalent to the continuation of the day's trading, which will affect the opening price of the next trading day.
Secondly, pre-market trading can also be conducted during abnormal opening hours. Outside normal trading hours, US stocks are also allowed to trade before the market, but whether to allow after-hours trading. Most US stock brokers are allowed to do pre-market trading, but there are also a few brokers who are not allowed or need telephone entrustment to do pre-market trading. This early transaction is not a stock but a futures, so don't generalize.
It is very important to consider the pre-listing price, liquidity and anchor price. Without a reliable anchor price, the risk of buying and selling is also high, especially for stocks with low liquidity. Therefore, the liquidity and price anchoring are the market index correlation and crude oil, which anchor the futures prices that have been traded all the time.
If the liquidity of the early market is not enough and it is the dominant market of retail investors, then on this special day, its volatility is more considerable than the regular time, so we should treat it positively.