Delta
How much an option's price moves for a $1 move in the underlying — the first and most-watched Greek. A delta of 0.5 means the option gains about 50 cents when the stock gains a dollar; it also tells you how many shares to hold to hedge.
Where this is taught
Definitions are the trailer. These free levels turn Delta into something you play — one bite-size lesson, with worked examples, a quiz and XP.