Delta

In short

How much an option's price moves per unit move of the underlying — also, loosely, its equivalent position ("100 calls, delta 0.5 ≈ 50 shares"). First of the Greeks.

Where Delta is explained in depth

The definition above is the short version. These pages put it to work, in the order they use it most:

Calculators that compute it

Terms this definition uses

The whole glossary

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