™A stock quoted with a $0.05 spread during the day may have a $0.50 spread after the regular session; the same order size can face a different execution environment.
Trading
After-hours trading
Trading that occurs after the regular exchange session, often with lower liquidity and wider spreads.
Plain-English context
Put the definition to work.
A last extended-hours trade is not a reliable executable price for your entire order; venue access and order rules differ.
Further reading and verification. Examples are hypothetical, not current quotes or recommendations. Product terms, tax treatment and market rules can change. FINRA — order types and execution