Delta is needed to estimate the amount of additional reward you will receive for purchasing a risky asset instead of a risk-free asset.

Risk-free Asset

An investment with a guaranteed return and no risk of financial loss.

Risky Asset

An investment that carries a significant possibility of losing some or all of its original value.

Delta

In finance, delta refers to the ratio that compares the change in the price of an asset, usually a derivative, to the corresponding change in the price of its underlying asset.