™Buying and selling a security in one session is an intraday activity. Margin-account requirements depend on the broker's current regulatory regime and house rules.
Trading
Day trading
Opening and closing positions within the same trading day, an activity involving significant risk.
Plain-English context
Put the definition to work.
Completing trades intraday does not eliminate gap, execution or leverage risk; cash and margin accounts follow different rules.
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