Premarket trading is the period before regular U.S. stock market hours, generally from 4 a.m. to 9:30 a.m. Eastern Time, when investors can buy and sell securities through electronic communication networks. This session allows traders to respond to earnings reports, economic data releases, and global market developments before the official opening. While it offers opportunities for early positioning, liquidity is often lower and price volatility can be higher compared to regular trading hours.