Delta

Delta is the options price sensitivity to price changes in the underlying asset.

If a call as .50 or 50 delta, and the asset moves up $1.00, the option will increase $.50 in value.

Another way to think about delta is a rough estimate of the probability of the asset finishing in the mney at expiration.

Our 50 delta call implies the asset has roughtly 50% chance of trading higher than our strike price on expiration.

Measuring delta is a way of calculating the equivalent position in the underlying asset.

If you are long 1 delta, you are effectively long one share of the underlying asset.