GLOSSARY // Day Trading
Gapper
A gapper is any stock set to open sharply away from its prior close — the trader's shorthand for the names a premarket scanner surfaces each morning. Most desks filter for a minimum gap (say 5%+), minimum premarket volume, and a price band that fits their strategy.
The morning gapper list is where day trading starts, because gappers concentrate the two things intraday strategies need: volatility and volume. A stock gapping 30% on 4 million premarket shares will trade more in its first hour than it normally trades in a month, which means fills are available and ranges are wide.
A 6:30 a.m. scan set to gap over 10%, premarket volume over 500,000 shares, and price between $2 and $20 returns three names. The top one is a $6.40 stock up 62% on an FDA clearance with 3.1M shares already traded — that becomes the primary watch for the open.
Related terms
Educational only — not financial advice. Definitions simplified for clarity; markets are messier than definitions.