In today's From Theory to Practice, Dr. Jim launches a three-part series exploring Delta, beginning with its textbook definition as a measurement of option price movements. While this is how Delta is taught academically, it's actually the least common application for active traders. Delta represents how much an option's price will move for every $1 movement in the underlying stock. Though often presented as a decimal (0.30), traders typically reference it as a whole number (30 Delta), meaning a $1 stock move leads to a $0.30 option price change. Long puts and short calls have negative Delta (bearish positions), while long calls and short puts have positive Delta (bullish positions). Understanding these relationships is fundamental for tracking option P&L and making position adjustments.